great review Brooko, thanks for your time.

Another great review, man!

Good review! I'm sorry to see that Aune made the RCA outputs fixed, rather than volume controlled pre-outs.  That's the only strike against it in my book, doggone it.  I had looked all over Aune's webpages but couldn't discern if those were pre-outs.

Yep - add a gain switch and option to go variable on the pot with the rear outputs, and this would be a serious contender as "THE" value dac/amp for 2015.

I went ahead and got the X1S, and have been pleasantly surprised at the sound quality.  It sucked me in to listening much longer than I planned, each time I sat down with it the past few days.  I resolved my one sticking point, by buying an Emotive Control Freak ($50 external volume control) to make the Aune also serve as preamp to my powered speakers.  Very pleased with the X1S!

That 10 ohm output impedance could be trouble...

Good idea Bill - it definitely has the ability to drive the active speakers, just not the inbuilt variable control.
 
@lamode - yep, for low impedance IEMs or cans with a susceptible frequency curve, there could be issues.  But with everything I tested, and even the 8 ohm 2000J, I was surprised at how good the X1S does sound.  So it's something to be aware of - but then again, I'm not sure how many people actually use IEMs with a desktop amp?  The ones that possibly would have issues would be the multi-driver TOTL IEMs with a lot of active crossovers. 

I've been listening to high (Senn HD600) and low (Denon AH-D2000) impedance headphones on the X1S.  They are, respectively, 300 and 25 ohms.  The Senns as expected sound great.  But the Denons sound better than I've ever heard them at home.  Subjectively, I'm having zero problem with the 10 ohm output Z.

Very great review, but I heard that the X1S produce some sort of low-volume hum. Is this true on your unit?

No hum at at all on my unit, not even with music stopped and volume turned up all the way.

@lehoang15tuoi - I ran same tests Bill did.  And sorry - I should have mentioned it in the review (don't know how I missed it).  It was dead silent for me.  Even with the DN2000J - which are very low impedance IEMs - no audible hiss that I could pick up - even with no music playing and volume up.
 
I'd suggest if someone is talking hum, then they have a ground-loop problem. And that could be more to do with their own wiring rather than the X1S

Wonder if there are gain control device on the market?

If anyone reading my experience with X1s, on one rare day I was shock to hear pop and clicks after a few days of use with on and off. Just off for a few mins and on, it came back fine. Appear to be MacBook software issue. Overall, X1s is really the best and simple headphone amp that work as plain as possible. The bad thing is I need more bass and brighter treble sound to bring back the magical details in Studio Ghili music (being perfectionist is a good thing), the only option is to change headphones with more low bass (not too much mids bass), sufficient mids, bright treble will solve.

I just got an Aune X1S.  I am concerned about the power output or whether there may be a defect, and I would like comments (pm me if you like).  In testing I used my Beyer 880 premium - 250 ohms with 96db sensitivity.  I notice others have had good luck with 300 ohm Senns.  But with the 880s I have the volume control at 5:00 o'clock or a little more.
 
In comparison my Schiit Magni 2 Uber drives the 880s fine with the level control about about 1:00 in hi gain.  Also, my Cayin C5 drives the 880s well in hi gain with the knob at 3.5 to 4 out of 9 settings on the dial.
 
One other thing:  when I un-boxed the X1S, the volume knob dropped off.  I have some small hex keys and was able to secure it with the line pointing to Min.  The line on the knob rotates well past Max all the way to 6:00 o'clock.  Is that normal? 
 
I will appreciate any thoughts.
 
Bruce

Hi - Bruce
The volume knob on mine goes from just before min to well past max - about 6 o'clock like yours.  So no problems there - it is normal.  As far as power goes, the X1S will put 200 mW into a 300 ohm load, and drives my 600 ohm T1 perfectly - so it should have no issues with your DT880.  A couple of things to check:
[1] Your actual listening level - if you are an extremely loud listener there is not a lot I can suggest other than turning it down.
[2] If you are using a PC - make sure the volume level on the PC is at 100% (in windows, use the volume mixer in the tray)
 
Otherwise I'd suggest talking to Aune.  It definitely doesn't sound normal.  Specs and all reviews I've read suggest this is quite a little powerhouse, and the DT880 (250 ohm) aren't a particularly hard load to drive.

The official site states only 80mw@300 ohm.
That is a big difference from 200mw stated here.
Which one is correct?