Introduction

First of all, I would like to thank Aune (@AuneAudio) for giving me the opportunity to review their unit.
This is the link to the relevant head-fi thread: https://www.head-fi.org/threads/fin...dsd-128-dac-amp-worldwide-review-tour.830399/.
I would like to mention that I am not affilitated to the Aune company in any way.

Associated Equipment, including Hardware and Software
Not a lot changed after the Aune X1S review. Anyway, these are my setups.

At Home
Hardware
Dedicated Mini PC with Intel Atom D510 1.66GHz (dual core, Hyper Threading)
Hardware: Supermicro X7SPA-H mainboard
Hardware: Linear PSU from italian brand ZetaGi (set @12V)
Hardware: 1x1GB + 1x2GB RAM
Software: Currently running Ubuntu Server 16.04, 64bit, Generic Kernel
Software: MPD (Music Player Daemon - http://www.musicpd.org)
Software: UPMPDCli (Upnp Renderer plugin for MPD - http://www.lesbonscomptes.com/upmpdcli/upmpdcli.html)

Gear
Schiit Wyrd

Gustard U12 USB Interface
Gustard X12 DAC
Gustard H10 Headphone AMP

Yulong D200 DAC / Headphone AMP
Aune X1S DAC / Headphone AMP with its own XP1 linear power supply

Additional software
Linux Mint 18.2 'Cinnamon' desktop PC, used to run GMPC/Cantata as MPD clients and Upplay as UpNP control point

BubbleUpNP on Android as UpNP control point

Another Debian-based Linux box is dedicated to file sharing (via Samba and via MinimServer, a UpNP server)

Cables
USB Cables: Audioquest Cinnamon 0.75m
HDMI Cable (I2S), used for the comparison with Gustard U12/X12/H10: Ricable HDMI Supreme F1
Balanced Cables, used for the comparison with Gustard U12/X12/H10: Neo By Oyaide D+ XLR
RCA Cables: Wireworld, Amazon Basics

Headphones and Speakers
Headphones:
Speakers Amplifier
Speakers

I have connected the Aune S6 to my dedicated PC via USB. Also, I have tried a AudioPhonics 5v LPS for USB power, with pleasant results. Not every DAC benefits from a dedicated LPS, because not every DAC draws power from the USB host. This one does. It seems to me the dedicated LPS can improve performances. I did not do any specific measurements, but what I can tell is that I have experienced in the past how a noisy usb power can harm the functionality of a DAC.

I also would like to mention tha, as usual, no drivers are needed on Linux.

In case someone wants to connect the S6 to a linux os, please note the name of the device is "DAC".

I tend to use upsampling with sox on mpd, tipically to 352.8kHz and 384kHz.

At the Office
Same old Linux PC with Intel Core2Quad Q6600 @office, also used with MPD (Music Player Daemon - http://www.musicpd.org), sox, upmpdcli, upplay.
Headphones: Sennheiser HD650 with a balanced cable.

The Listening
I listened as much music as I could in the limited time available. Here are the albums I'd like to specifically mention:

• Dire Straits - Brothers in Arms
• Miles Davis - Kind Of Blue (from HDTracks, stereo version)
• Metallica - The Black Album
• Eric Clapton - Unplugged

Please not that I did not listen to the HD800 with the S6 in balanced mode as I do not have a cable yet.

Impressions

• Deeper (but not bloated) bass
• Lots of power (this kind of explains previous bullet)
• No harshness to my ears, at least after 2-3 hours of listening.

Be prepared for 2-3 hours of not-so-exciting listening time, so I would advice to allow some burn-in time when possible.

The listening has been very pleasant. I enjoyed the bass definition, which probably comes from a great reverse of power.
Also, the mids have always been good and I never heard any harshness on the highest frequencies.

My only complaint is I could not properly test this dac/amp with the HD800 in balanced mode. I hope I will be able to fill this gap soon.

Comparisons
I have compared the S6 against the following two setups:

• The Aune X1S
• The Gustard U12/X12/H10 stack

Both the X12 and the X1S use ESS chips. The X12 adopts the 9018, while the X1S adopts the mobile version 9018k2m.

The Aune S6 adopts a DAC chip from a different brand: the AKM AK4495 from Asahi Kasei.

Detailed specs of the S6 are available on the aforementioned Aune forum post. As I have done with previous reviews, in order to avoid mistakes and misunderstanding, I prefer not to duplicate technical specifications here.

Against the Aune X1S
Quite easy to imagine, this is not a fair comparison. The S6 is superior in quite every aspect. This consideration is not in any way intended to be detrimental to the X1S.
Simply, these two products belong to different price ranges, and the different in audio quality is well audible. That said, I still own and enjoy the X1S in my setups.

Against the Gustard U12/X12/H10 stack
It has been very difficult to compare, especially because I feel using the HD800 with the single ended cable on the S6 would not have been fair.
I can say I have compared the HD650 single ended from the U12/X12/H10 against the HD650 balanced from the S6.
Despite a higher price, I feel the S6 can get very close to the Gustard Stack. We also need to consider the S6 is not burned-in as the Gustard stack is. Also, the H10 has been upgraded with Burson Supreme Op-Amps (both single and dual), for a great improvement.
Both of the setups rewarded me with very nice sound, with no harshness whatsoever, with great definition and great control. In terms of raw power, the S6 seems to have an advantage here.

Why would I want to buy it?
Because it's a very nice dac/amp, remarkably powerful, and because I want a balanced headphone out
It has a variable output so I can also think of connecting a speakers power amp (meaning, with no pre-amp section)

Final thoughts
I really liked the Aune S6 and I want to thank Aune again for the opportunity and the patience.
One thing that is IMO left to be desided by this unit is the lack of a I2S input. If you have a DDC like the Gustard U12 or the now very popular Singxer, you might want to use the I2S of such interface, but the S6 has no I2S input.
You can use the coax, aes/ebu or the opt input, but those kind of connections are limited to 192kHz max (this happens on almost all DACs I know of, with the notable exception of some Chord DACs).
Of course this is not a showstopper: the usb input is really fine, and can be improved with dedicated LPS as well as with some "jitter eliminator" devices, like, for example, the Schiit Wyrd.
Another minor glitch IMO is that you do not have the option to output to headphone and line outputs at the same time. However, I understand why it is designed like that. In most use cases, one does not want to ear speakers when listening to headphones.
So in conclusion, I would safely advise a friend to buy this DAC/Amp and I would be sure he would not complain.

Great work, again. Kudos to Aune.

Introduction

I bought the full Gustard Stack early this year, after long work of selection and long time spent reading the corresponding threads on head-fi as well as other sources.
The stack is composed of the U12 (a USB interface), the X12 DAC and the H10 headphone amplifier.
Recently I upgraded the H10 with a full Burson V5-OPA-D / V5-OPA-S op-amp Kit. I used both the single "S" and the Dual "D" series of the OP-AMPs. A total of four pieces, to be clear.
TL;DR: An AMAZING upgrade for an already very good amplifier!
 

 

 

Associated Equipment, including Hardware and Software

 

Hardware

Dedicated Mini PC with Intel Atom D510 1.66GHz (dual core, Hyper Threading)
Hardware: Supermicro X7SPA-H mainboard
Hardware: Linear PSU from italian brand ZetaGi (set @12V)
Hardware: 1x1GB + 1x2GB RAM
Software: Currently running Ubuntu Server 15.04, 64bit, Low Latency Kernel
Software: MPD (Music Player Daemon - http://www.musicpd.org)
Software: UPMPDCli (Upnp Renderer plugin for MPD - http://www.lesbonscomptes.com/upmpdcli/upmpdcli.html)
 

Gear

Schiit Wyrd
Gustard U12 USB Interface
Gustard X12 DAC
Gustard H10 Headphone AMP
Burson V5-OPA-D
Burson V5-OPA-S
 

Additional software

Windows 7 desktop PC, used to run GMPC/Cantata as MPD clients and Linn Kinsky/Kazoo as UpNP control point
BubbleUpNP on Android as UpNP control point
Another Debian-based Linux box is dedicated to file sharing (via Samba and via MinimServer, a UpNP server) 
 

Cables

USB Cables: Audioquest Cinnamon 0.75m
HDMI Cable (I2S): Ricable HDMI Supreme F1
Balanced Cables: Neo By Oyaide D+ XLR
 

Headphones

Headphones: Sennheiser HD650; Sennheiser Momentum On Ear; Denon AH1001; Yamaha HP-3 (Orthodynamic, modded)
 

The setup

All listening tests were made using the mentioned dedicated Linux box with mpd, either with the mediation of upmpdcli or natively.
The Linux box also benefits of a Schiit Wyrd, which supposedly "cleans" the usb signal and has its own separated power supply, isolating the DAC from the noisy PC environment. 
In my experience, the use of the Schiit Wyrd is very effective, altough the improvement is less evident when used before a dedicated interface like the Gustard U12. I consider the Schiit Wyrd one of my best audio purchases ever.
I find the Linux setup so clearly superior to the Windows counterpart that I do use the latter only occasionally: the Gustard X12 is connected via usb to the desktop PC, while the Gustard U12 is connected to the Linux box, with the Schiit Wyrd in the middle.
I also used upsampling @352.4kHz and @384kHz with sox, alternated with a more native configuration (a.k.a. bit perfect).
 

The Tracks

For this review, I mostly used the following tracks:
Carlos Santana - 'Aqua Marine' from 'The Ultimate Collection'
Miles Davis - 'So What' from the 1959 album 'Kind of blue', purchased on HDTracks (24bit/192kHz)
Eric Clapton - 'Tears in Heaven', 'Running on Faith', 'Layla', and really most tracks from the 'Unplugged' album
Dire Straits - 'Money for nothing' and 'Brothers in Arms' from the omonimous album; 'Fade to Black', 'Planet of New Orleans', 'My Parties' from the album 'On Every Street'
Janine Jansen - 'Le quattro stagioni' (Antonio Vivaldi), purchased on HDTracks (24bit/96kHz)
Rebecca Pidgeon - '24 hours of love', 'Primitive Man' from the album 'The New York Girl's Club', also purchased on HDTracks (16bit/44.1kHz only, sadly)
Sting - 'Consider me gone', Moon over Bourbon street', 'Fortress around your heart' from the album 'The Dream of the Blue Turtles'; 'They dance alone', 'Little wing', 'History will teach us nothing' from the album '... Nothing like the sun'
Sting - 'A thousand years' from the album 'Brand New Day'.
All the tracks come from flac files ripped from my precious personal CD collection with Exact Audio Copy, except when otherwise noted (HDTracks downloads).
Of course other tracks were used, these being the most relevant ones.
 

The Listening

The H10 is currently my best headphone amp. I like it a lot. It has the power to drive my current headphones (the best being the Sennheiser HD650) effortlessly. It can also drive my vintage Yamaha HP-3 (orthodynamic) quite well.
Before the H10, I was using the headphone output of the Yulong D200 DAC/Amp. Switching to the Gustard U12/X12/H10 has been a very relevant upgrade, in terms of both transparency of the DAC and output power of the amplifier.
My favourite albums now sound smooth and lush, and more dynamic than before. Also detail retrieval is on higher levels than with the Yulong D200 (a unit I still love though).
I never noticed any channel imbalance, even at low volumes. 
The H10 is very equilibrate, not bright, but not even too dark. 
The bass impact is notable but not bloated or muddy; instead, I would say it's precise and tight. Also, the bass response is tight even with low-impedance headphones like the Sennheiser Momentum On-Ear: those phones may sound quite muddy if the amplifier has high output impedance. For example, they don't sound good with the SMSL SAP-III, which in reality is targeted to high-impedance headphones only.
There is a good extension on higher frequencies (as far as I my hearing can sense) with no harshness.
Quite a nice amp though. 
Then the Burson Op-Amps came in.
Here you can find some photos (already show on this post: http://www.head-fi.org/t/735828/gustard-h10-high-current-discrete-class-a-output-stage-headphone-amplifier/3450#post_12053024)
 


 
 
 
 
 
 

 
The installation has been very simple and straightforward.
So, what changed?
Well, pretty much everything, and for better!
The most obvious enhancements are, IMO, in clarity and smoothness. Details are not lost in this smoothness, and instead I actually noticed more details than with the stock op-amps.
Every track I played is now more 'live', more real and definitely more natural. 
All the tracks from the album 'Unplugged' by Eric Clapton have never sounded so natural and detailed to my ears. Toe-tapping and the sense of rhythm is at its best.
The bass on the beginning of the track 'A thousand years' from Sting's album 'Brand New Day' is simply amazing now.
I realize how good the H10 sounds also by the fact I need less volume to enjoy good sound. This, IMO, indicates a clearly better clarity level given by the Burson Supreme V5 Op-Amp sets.
It's like having a completely new amp!!!
Don't get me wrong, I still think the H10 is a complete bargain. The thing is that with these op-amps it really reaches a new level.
The good thing is that you can start (relatively) cheap and upgrade it very easily.
 

Final thoughts 

The H10 is a wonderful amplifier. It can drive pretty much every headphone, maybe with the exclusion of the Hifiman HE-6: anyway those headphones are on the extreme of the range.
It will deliver hours of pleasure and will let you discover again your music collection. At a price lower than 400USD, it is really a no-brainer: I think you will not regret it.
With the Burson Supreme V5 Op-Amps, it becomes even better, under every possible aspect. 
This amp has a good number of fans (myself included). You can find a dedicated thread on head-fi at this URL: http://www.head-fi.org/t/735828/gustard-h10-high-current-discrete-class-a-output-stage-headphone-amplifier
 
 

Introduction

First of all, I would like to thank Aune (@AuneAudio) for giving me the opportunity to review their unit.
This is the link to the relevant head-fi thread: http://www.head-fi.org/t/777650/aune-x1s-32bit-dsd-dac-worldwide-review-tour-reviewers-wanted.
I am not affilitated to the Aune company in any way; the tour ends with five units delivered for free to the author of the best reviews:
 
    Five luckly winners will be  chosen to get a set of X1S DAC for free according to the reviews 
 
As you will probably notice if you will read the review entirely, I ended up liking this unit.
Of course, I would be happy to win one, but I will not try to do so by overly exagerating its good features while hiding its defects and/or limitations.
Instead, I will try to win by describing, in the most honest and thruthful way, the five days I could spend with this unit. 
Please not that English is not my first language, so I hope the errors in this text will not make the reading too annoying.
 

Associated Equipment, including Hardware and Software

At Home

Hardware

Dedicated Mini PC with Intel Atom D510 1.66GHz (dual core, Hyper Threading)

Hardware: Supermicro X7SPA-H mainboard
Hardware: Linear PSU from italian brand ZetaGi (set @12V)
Hardware: 1x1GB + 1x2GB RAM
Software: Currently running Ubuntu Server 15.04, 64bit, Low Latency Kernel
Software: MPD (Music Player Daemon - http://www.musicpd.org)
Software: UPMPDCli (Upnp Renderer plugin for MPD - http://www.lesbonscomptes.com/upmpdcli/upmpdcli.html)
 

Gear

Schiit Wyrd
 
Gustard U12 USB Interface
Gustard X12 DAC
Gustard H10 Headphone AMP
 
Yulong D200 DAC / Headphone AMP
 

Additional software

Windows 7 desktop PC, used to run GMPC/Cantata as MPD clients and Linn Kinsky as UpNP control point
BubbleUpNP on Android as UpNP control point
Another Debian-based Linux box is dedicated to file sharing (via Samba and via MinimServer, a UpNP server) 
 

Cables

USB Cables: Audioquest Cinnamon 0.75m
HDMI Cable (I2S), used for the comparison with Gustard U12/X12/H10: Ricable HDMI Supreme F1
Balanced Cables, used for the comparison with Gustard U12/X12/H10: Neo By Oyaide D+ XLR
 

Headphones and Speakers

Headphones: Sennheiser HD650; Sennheiser Momentum On Ear; Denon AH1001; Yamaha HP-3 (Orthodynamic, modded)
SMSL SA-50 amplifier
JBL Control One speakers.
 

At the Office

Linux PC with Intel Core2Quad Q6600 @office, also used with MPD (Music Player Daemon - http://www.musicpd.org).
Headphones: Sennheiser HD650.
    

Unboxing

The first thing I noticed, looking at the box, is that the Aune brand is symmetric. Nice!
I then realized (after reading WayneWoondirts' review) that I was not the first to notice this curious fact. Still, that reading led me to know the Aune logo is actually an "ambigram" (https://en.wikipedia.org/wiki/Ambigram): I didn't even know the term. Thanks, WayneWoondirts.
The box is appropriate in size, everything has its place. Sometimes happens that when you need to put everything back, you wish you had a bigger box. Luckily this is not the case.
The PSU is 220V, and has plugs suitable for my area (Italy). So no adapters needed: good! 
The other thing I immediately noticed is the nice design of the DAC itself. My wife liked it, too.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Description

The unit is quite small, and can fit nicely on most desktops. It feels very sturdy.
The PSU is quite big and bulky, but luckily its conformation does not require to connect it directly to the wall, having a power cord (non detachable) instead, on both sides. The cords are long enough to comfortably place the PSU away from the desk area. So no big issues here.
The side panel curves are similar to the one on the volume knob: a nice touch! The unit IMO is aesthetically very pleasing.
Its curved top surface might be an issue if you plan to stack something on it; of course, you can stack the Aune X1S on other (supposedly flat) unit without issues. During my tests, I stacked the X1S on a Yulong D200.
The volume knob itself, while it does not offer a lot of resistance to the rotation, feels well implemented. During the listening session, I did not notice any amount of channel imbalance.
The front panel is very simple: a simple selector (which also controls the active filters), the headphone 6.3mm socket and the volume knob. A 3.5 to 6.3mm adapter is included.
The Aune gets only slightly warm even after many hours of usage.
On the back side, you can find the usual power connector, the USB type B socket, two SPDIF inputs (Coaxial and Optical), a Coaxial output (quite unusual on this kind of products). Also, there is a couple or RCA analog output (fixed level) as well as a couple of RCA input.
So the unit can be used as a DAC alone as well as a headphone amp alone.
Some people complained about the analog output being fixed: if you want to connect speakers, you need either an amp (as in my case), or powered speaker with indepent volume control.
Of course, if the output had been variable, someone would have complained because it is not fixed. You can't please everyone.
Very few DACs have both variable and fixed outputs. Personally, I prefer the fixed option because I use an amp to drive my desktop speakers.
Also, implementing both options would surely raise the final price, so I think Aune made the right decision.

 

Specifications

I do not want to replicate the specifications page you can find on Aune's site.
What's worth mentioning, and what probably people expect to find in a review, are the supported formats and the adopted DAC chip.
The DAC chip is, accordingly to the specs, a Sabre ESS9018K2M.
The device supports all sampling rates up to 384kHz (including 88.2, 176.4, 352.8 as well as, of course, the usual 44.1, 48, 96, 192).
 

The setup

All listening tests were made using the mentioned dedicated Linux box with mpd, either with the mediation of upmpdcli or natively.
The Linux box also benefits of a Schiit Wyrd, which supposedly "cleans" the usb signal and has its own separated power supply, isolating the DAC from the noisy PC environment. 
In my experience, the use of the Schiit Wyrd is very effective, altough the improvement is less evident when used before a dedicated interface like the Gustard U12. I consider the Schiit Wyrd one of my best audio purchases ever.
I find the Linux setup so clearly superior to the Windows counterpart that I do use the latter only occasionally: the Gustard X12 is connected via usb to the desktop PC, while the Gustard U12 is connected to the Linux box, with the Schiit Wyrd in the middle.
I also used upsampling @352.4kHz and @384kHz with sox, alternated with a more native configuration (a.k.a. bit perfect).
Another advantage of using Linux is that you do not need to install any driver. Using multiple dacs on windows can be very annoying if not a nightmare. Try dealing with 3-4 XMOS control panels that all look the same (distinguishable for the different version numbers, when you're lucky enough) one for each XMOS based DAC you ever connected. 
Definitely not funny. Not so with Linux!!
So, I did not use the usb flash drive at all. However, it is a nice touch, since it is more likely that new PCs do not come with an optical drive.
 

 

 

 

 

 


 

The Tracks

For this review, I mostly used the following tracks:
Carlos Santana - 'Aqua Marine' from 'The Ultimate Collection'
Miles Davis - 'So What' from the 1959 album 'Kind of blue', purchased on HDTracks (24bit/192kHz)
Eric Clapton - 'Tears in Heaven', 'Running on Faith', 'Layla', and really most tracks from the 'Unplugged' album
Dire Straits - 'Money for nothing' and 'Brothers in Arms' from the omonimous album; 'Fade to Black', 'Planet of New Orleans', 'My Parties' from the album 'On Every Street'
Janine Jansen - 'Le quattro stagioni' (Antonio Vivaldi), purchased on HDTracks (24bit/96kHz)
Rebecca Pidgeon - '24 hours of love', 'Primitive Man' from the album 'The New York Girl's Club', also purchased on HDTracks (16bit/44.1kHz only, sadly)
Sting - 'Consider me gone', Moon over Bourbon street', 'Fortress around your heart' from the album 'The Dream of the Blue Turtles'; 'They dance alone', 'Little wing', 'History will teach us nothing' from the album '... Nothing like the sun'
All the tracks come from flac files ripped from my precious personal CD collection with Exact Audio Copy, except when otherwise noted (HDTracks downloads).
Of course other tracks were used, these being the most relevant ones.
I also used some demo DSD tracks to test the functionality with each and every possible operational modality (e.g. all sample rates) of the X1S.
 

The Listening

Now, the fun part. I prepared a short playlist and connected my faithful Sennheiser HD650 to the Aune X1S.
The first listening was really a pleasant surprise! I did not imagine to be gratified by a sound so detailed, rich and non fatiguing. Also, the soundstage is so immersive.
Listening to Santana's 'Aqua Marine' was real good. I used this track multiple times during the comparisons with my other systems. A great sense of depth was clearly perceivable. It was a please to hear fast changes from quite to loud passages.
Miles Davis' 'So what' from HDTracks @192kHz flows nicely and natural, an incredible track. Miles' trumpet is very real and I had the impression to be present in the recording studio.
Eric Clapton's classical 'Tears in Heaven', 'Layla', 'Running on faith' from 'Unplugged' (as well as all the other tracks: that album is really amazing...) sound live, detailed, vibrant and dynamic as they should. Some background noise, present in the tracks at times, tells the listener how natural the recording actually is. It feels like you can see Eric touching those strings and tapping his feet.
'Le quattro stagioni' played by Janine Jansen are fast, detailed and dynamic. Again, this recording is live and natural. The player's breathing is clearly audible, the violin sound is so sweet and natural, while the continuous bass sustains the performance wonderfully.
I also especially like the indicated Dire Straits' tracks (as well as many others) for the clean and elegant executions. In particular, while 'Brothers in arms' is one of the tracks I always greatly enjoy, the tracks from 'On Every Street' are exceptional in the quality of the execution, so lush, warm, expansive. The Aune X1S renders them very well! It is a very relevant test for me.
The same mostly applies for the Sting tracks. In particular 'Fortress around your heart' is a best favourite, for the nice soundstage with instruments' positions so definite. Also, I like Sting's voice a lot. I enjoyed a nice refined reproduction with the X1S.
During the tests, I used other headphones too.
In particular, the Sennheiser Momentum sounded very nicely with this dac/amp. I know how easily the Momentum can play with a really bloated and confused bass if the amplifier has non-optimal output impedance. In particular, they sound almost unlistenable with the SMSL SAP-III, which is in fact targeted to high-impedance headphones. In case you wonder, no, there is no comparison between the SMSL SAP-III and this Aune X1S. The Aune X1S is simply in another league.  
I also used the Denon AH1001. No surprises here: these are decently sensitive headphones (more than the Momentum On Ear, or maybe their isolation is better, or maybe both!). Decent neutral sound.
The Yamaha HP-3 are not very sensitive and are around 150ohm of impedance. In my opinion, the X1S lacks some power when driving those. Still, it drives them to good levels, but something is missing.
I also used, for a small amount of time, the SMSL SA-50 amplifier to drive the JBL Control One speakers. No surprises, the sound was nice, deep and detailed as expected.
So, is everything ok and aligned to the expectations, and even beyond? Sure. The Aune X1S seems a perfect companion for serious headphone listening.
Does it smash any competitor in any category? Well, not so fast...
 

 

 

 

 

Comparisons

Of course, I compared the Aune X1S to my other gear: the Yulong D200 and the full Gustard Stack (U12/X12/H10).
The Schiit Wyrd was used for ANY of the mentioned configurations.
 

Versus the Yulong D200 DAC/Headphone Amp

Compared to the Yulong D200, the X1S performs very well. The detail on the D200 is a hair better IMO, and the sound signature is quite similar (after all, they are both ESS Sabre Chips, ESS9018K2M for the X1S and ESS9016 for the D200). Where the D200 shines against the X1S is the output power, which is probably responsible for tighter bass. The D200 has more body and handles dynamic passages with more ease. It feels like the D200 has more 'control' on the music.
Of course, it's a bit unfair as a comparison, as the price of the D200 is more than 2X the price of the X1S.
 

Versus the Gustard Stack (U12/X12/H10)

Where there is not chance for the small X1S is when I compared it to the Gustard Stack. Simply, the Gustard stack is on a higher level. More power, more depth, more details. Almost every aspect is inevitably better on the Gustard stack. In this case, again, the comparison is sort of unfair. The Gustard stack is composed of separated interface, dac and amp. The size of the kit is enormously different and the price is about 4x the price of the X1S. 
But, paradoxally, it was this test that showed me the real value of this X1S: for 1/4 of the price of the Gustard Stack, the performance is surely enjoyable and pleasing. In fact, like other uses, I think the X1S has considerably raised the bar of 'entry level' quality, and that's really a good thing. Further competitors in the 200-300$ price range will have to be able to at least not disappear against the X1S.
 

Versus some other Stuff

At the office, I am using my FiiO X5 as a usb dac with a Epiphany Acoustics O2 headphone amplifier. In this case, yes, the X1S is clearly better. Awesomely better. The X1S has more functionalities (up to 384kHz sample rate support, and DSD support), more quality, more detail, wider soundstage, more power, a nice pleasant design. More everything. 
Plus, it's a one-piece kit, perfect for office use.
Previously, I was using a SMSL Sanskrit with a SMSL SAP-III (mentioned before). No contest here, the X1S beats this kit hands down.
 

Concerns about the PSU quality were expressed on Head-Fi.org

Some users expressed concerns about the PSU quality. They say the stock PSU is a SPSM, and therefore not suitable for an audio device. AFAIK, a SPSM is not bad per se, but usually a linear power supply should be a better choice. That said, it seems to me that adopting such a PSU would have raised the price of the X1S considerably. 
Still, in case Aune decides to disclose the specifications of the PSU (which seems to me to be dual, but I am no expert), adopting linear PSU might be a nice upgrade.
Anyway, I did not notice any issue that can be related to the PSU: no background noise is audible to my ears, and it seems that the PSU is good enough. I don't know for sure if a different PSU solution would add some grunt to the amp module.  
 

Conclusion

Again, I want to say "Thank you" to Aune for the opportunity of having the X1S for some days of testing.
The Aune X1S is a very nice concentrated of audio technology. It will surely please anyone looking for a compact all-in-one solution in the 200-300$. I cannot make comparisions with stuff I do not own, but considering how close it is to the Yulong D200, I think its value can surpass many if not most current DAC/AMP in the 300-500$ range with ease. It is just an speculation, but I am quite confident of it.
The X1S is detailed, powerful enough (unless you use very difficult headphone: I think, for example, that the HifiMan HE-6 are out of reach here), it offers a good soundstage, and delivers hours of non-fatiguing listening pleasure. Definitely a bargain for the required price. 
Congratulations Aune, well done.