UPDATE 23/3/2015:
I'm still using this DAC which makes it the longest used digital component in my system to date! I will probably be upgrading to something new as a streaming solution, but this will almost be an order of magnitude more expensive (> EUR 4.000). The fact that I haven't found a meaningful way to upgrade in the mean while and anywhere near the price is a strong testimony to the quality of this DAC in conjunction with the SBT.
 
======================================== Original review ==================
 
General
I bought this DAC as an upgrade from the Maverick Audio D1 that I've used for the past year in my main system. I really liked the NFB-2 from day one so I decided to put a bit more effort into writing a review. In order to get some 'old world HiFi' reference point I extensively compared this DAC to an Arcam CD37.
 
The test setup can be found at the end of this review.
 
Construction
The NFB-2 is solidly build. All connectors and switches have a quality look and feel to them. Connectors are good quality and perfectly fit the WBT connectors on my cables.

The PCB layout and wiring is well made with attention to detail. The high quality components such as Wima capacitors and Vishay resistors are pretty unique in this price range. I didn't feel the urge whatsoever to grab my soldering iron and start 'upgrading'  some key components
 

Sound

I've mostly listened to the NFB-2 with my main speaker system using the SB Touch as source. I've compared it to an Arcam CD37 and my TC-Konnekt  D24 and Maverick D1.
 
My initial impression was something like: a warm sounding DAC with an impressive soundstage, lots of micro detail and a well defined and extended bass.This first impression was mostly confirmed over the past few weeks of listening and comparing.
 
Timbre/tonal balance
The NFB-2 has an overall smooth/warm character. My main system has a relatively bright character and my STAX SR-404 is quite neutral. The NFB-2 proved to be a great match for both systems. 
Its always difficult to use particular words to describe tonal balance. In this case warm does not imply particular coloration in the mid-low frequencies or top-off highs. Its much more the absence of any sibilance or ringing in the mid-high frequencies. The female voices of Jenifer Warnes, Ana Caram, Rebecca Pidgeon are beautifully represented. Jenifer Warnes does not have the sharp edges in ' Song of Bernadette' that I've heard in many systems. The soprano vocals and strings in the Bach recording show great extension, but never get edgy or grainy.
 
This even gets better with 24/96 recordings. I have the song 'Spanish Harlem' both in 16/44 and 24/96 the original CD version sounds great. But the 24/96 opens up a whole new dimension in terms of micro level detail but also in smoothness and HF extension. The passage where the violin starts playing (at 1:48) is a nice example. The NFB-2 shows superb extension and detail without ever getting harsh. And the improvements that HD provides are more significant then when using my TC-Konnekt or D1.
 
Bass
This is a strong point of the NFB-2. This DAC provides bass with very deep extension, great detail and control and some serious weight. I've never heard all these qualities in one unit at this price range. The CD37 is perhaps slightly better, but at more than 4 times the price! The D1 lacks the extension and weight. The TC-Konnekt does provide some weight, but at the expense of definition.
The bass line intro of Spanish Harlem shows no resonance or coloration. The  bending on the bass table on Ganges Delta Blues from Cooder and Bhatt is reproduced with great precision. And the 'genie'  on Three Wishes of Roger Water rolls over the ground with an unmatched impact. 
 
Midrange
The midrange is where my NFB-2 improved most over the last 100-200 hours of playing. Initially it was just nice, nothing great. Over the past week I've heard it evolve into a very lush, open and dynamic midrange. Vocals, guitar and sax have a tangible quality to them. Jennifer and Sara K stand nicely in front of the soundstage, without being blown into bigger than life proportions. This is also the part where IMO the NFB-2 outclasses all 3 other sources that I compared it with. It is in a completely different league than the TC-Konnekt and D1. And it outperforms the Arcam by some margin. It almost has a tube-like presence and warmth, but without the coloration (often resulting in 'bigger than life' vocals and saxophone) that usually comes with that.
 
High frequencies
HF is smooth and extended. This can be particularly noted on the Matheus Passion and the higher pitched voices on the Chesky album Cymbal crashes and Hi-hat strokes are open and bright with good attack. Even while the overall tonal balance is smooth and warm, the highs have great extension and refinement.
 
Soundstage and precision
The NFB-2 provides a very large soundstage. Wider than I've heard before on my system. The CD37 gives slightly more depth, but only at 16/44 recordings. When switching to 24/96 (on the Ry Cooder album and ith 'Spanish Harlem') the NFB-2 wins hands down on all spatial aspects of the sound stage (width, depth and instrument separation). The background sounds/noises on the start of Spanish Harlem give some beautiful cues about the size of the room. The voice of Livingston Taylors is warm and has a chesty low end but is also very detailed. Articulation noises are clearly presented. The breathing, the lip noises and the airy quality of his whistling are fascinating to listen to. And I have not heard it in this detail before on my main system or my Stax.
 
Inputs
I used the SPDIF Coax input with the Logitech Touch as the source most of the time. My NFB-2 has the WM8805 digital input receiver, and I have not compared it to the DIR9001. Many headfiers say that the DIR9001 is notably better than the WM8805. I also did some testing with USB and Optical.

 
NOTE: the front pannel has DAC-19 as type, but the DAC is actually a NFB-2. Audio-GD had some face plates left and used them for the the first production run of the NFB-2.
 
Both USB and Optical where less good than SPDIF Coax. When compared to the D1 the NFB-2 clearly has a better USB receiver. The difference between the two DAC's is bigger using USB then when using the SPDIF input. The NFB-2 does a much better job here.  The same is the case for the Optical input (source being a rather jittery MacBook Pro). 
 
I also tested the NFB-2 while using my TC-Elektronik as a FireWire to SPDIF converter on my Macbook. This combo resulted in a slight improvement of the spatial imaging and HF refinement compared to the SPDIF output of the SB Touch. But I had to switch back and forward several times to hear this. In the past I've come to the conclusion that the TC-Konnekt is a high-quality SPDIF source. Based on this I draw the conclusion that either the NFB-2 has a pretty robust SPDIF input or the SB Touch also has a high quality SPDIF output.
Conclusion: the USB input is not bad at all, but no match for the SPDIF-Coax (when using a good source!). And the TC-Konnekt is a much better computer-SPDIF interface than the built-in part of the NFB-2, though with a less versatile FireWire connection. 
 

 
Overall Conclusions
This is a great DAC at this price point. It matches perfectly with my main system and my Stax phone. In particular at this price level. I've compared it directly with an Arcam CD37 in my system. I found this a very intriguing comparison. I've always found the Arcam CD players to be high performers. The CD-37 uses the same DAC topology (dual WM8741) which makes it an interesting reference point. Compared to this player the NFB-2 is overall at the same quality level. The NFB-2 has slightly more open and transparent mids and the CD37 a bit more refined highs. When using HD material the NFB-2 wins hands down.
The comparison with my Maverick D1 (using OP249) and TC-Konnekt D24 is really not fair. The NFB-2 is in an entirely different league in almost all aspects (bass, mids, spatial imaging, detail).
 
My most notable conclusion is in an entirely different area. I've had various discussions with friends lately about streaming audio. They are convinced that it can't get anywhere near a good CD player. My newest setup (SB-Touch > NFB-2) has convinced me that streaming audio can be at least on par with a high quality CD player. And even improve on it when play the HD version of the same recording (which the CD-player is simply not able to playback). It all depends on a good transport/source (which the SB Touch clearly is) and a good DAC. 
 
The strong points  of the NFB-2 are:
- smooth sound without missing out on detail
- fluid mids
- weighty, well defined bass
- the widest sound-stage I've heard to date
- great on HD material
 
I haven't really found any clear shortcomings. In particular when considering its price. Perhaps in some systems that are a bit bass heavy, the bass of the NFB-2 might be a bit too much. And if you want to make maximum use of the NFB-2 with a computer source, it pays off to invest in a USB>Coax interface such as the Audio-GD DI. As a secondary input the USB input of the NFB-2 is quite OK.
 
I think this DAC will prevent me from upgraditis for quite some time to come!
 
Test setup
Sources:

1. Logitech SqueezeBox Touch
2. Macbook Pro > Toslink
3. Macbook Pro > TC-Konnekt > SPDIF-Coax
4. Arcam CD37 > SPDIF-Coax

 
System:

1. Preamp: DUSON C1000
2. Power Amp: DUSON A-10
3. Loudspeakers: Epos M22i
4. Cables: Straightwire Rhapsody interconnect, Van den Hul Videolink digital interconnect and Nordost Blue Heaven LS
5. Phones: Stax SR404 + SRM-Xh (I've sold my SRM-1 and use this for the time being) and some occasional listening with my Shure E3c and AKG K271 (trough the C1000).

 
Music:

1. The worlds greatest Audiophile vocal recordings - Chesky Records 24/96  (Rebecca Pidgeon, Livingston Taylor) / Rebecca Pidgeon also on 16/44
2. Jenifer Warnes - Famous Blue raincoat ('07 edition) 16/44
3. Ry Cooder & V.M. Bhatt - A meeting by the river 24/96 & 16/44
4. Roger Waters - Amused to Death 16/44
5. Mattheus-Passion - Philippe Herreweghe - Harmonia Mundi 16/44

 

 
After following the discussion on this forum for a few weeks I decided to go for the D1. I've input from many of you to be very helpful. Thanks for that!
 
I was looking for an amp/dac that could for the time being replace my TC-electronic Konnekt D24. I haven't read much about this device around here. For me it has been a reliable and high quality work horse in my private project studio. But since I wanted to start streaming audio to my main system in the living room, I've abused this DAC/amp for that.... I have a Philips NP2900 with the digital output connected to the DAC. The last few months I am using the Konnekt more and more in my studio/rehearsal room. And decided to move it back there.
 
I believe that audio streaming on a real High-End level is only just starting to develop (I've heard the Naim Uniti in my system and wasn't impressed. So I want to wait some time until this technology gets more mature. And work with something on a significant lower budget in the mean while. 
My specs: I wanted a simple black box with a volume control, a straightforward input selector, analog AND digital input and preferably a good headphone output to drive my AKG K271, Shure E3c and a few lesser headphone specimens lying around in my house. Oh yes, it would be great if it could drive my DUSON A10 poweramp and my STAX SRM-1 to
 
Well, the D1 is 'just what the doctor prescribed' in terms of inputs/outputs/selection/volume control. But does it deliver the sound quality? 
 
My music taste ranges from a broad spectrum of classical music (Bach to Strawinsky), Blues, Jazz, Rock and once in a while some straightforward pop music. Some albums I've always used for listening sessions are:
- Jenifer Warnes - Famous Blue Raincoat
- Sara K. - Hobo
- Haitink/Ashkenazy - Brahms 2nd pianoconcerto on DECCA
- Herreweghe - Bach Matthaus Passion on Harmonia Mundi
- Roger Waters - Amused to Death
- Pink Floyd - Delicate Sound of Thunder
- (?) - Jazz at the Pawnshop 
- Van Morrison - It's to late to stop now (live)
(yes I know, Im getting old)
 
I've mainly based this review on listening trough the following setup:
NP2900(digital out) > D1 > DUSON A10 > Epos M22i
 
My initial impressions (out of the box):
A pleasant sounding dac-preamp that delivered smooth highs, fluid mids and reasonably good bass extention. But I found it to seriously lack depth and detail. The tube output gave a slightly more 'open' sound, but not really more detail in mid and high. The bass on the tube output was less focussed and tight.
After a few days the mids improved a bit, they became more open an detailed. The bass seemed slightly more tight (best noticeable on the Roger Waters CD). On the tube output the difference was bigger and more apparent. There was a clear extention of the bass response and the midrange opened-up seriously. A much deeper and wider soundfield. But still I found details (in particular on the classical CD's) lacking. The good news was that I didn't find any clear flaw either (no boomy bass, no nasal mids, no shreeking HF).
Compared to the Konnekt D24 It was an easy choice: the Konnekt is much better in terms of HF detail, soundstage and bass extention.
 
After lots of reading on this forum I had become quite interested in experimenting with OpAmp rolling..... I had two options available for the line-out: OPA627 and OPA249. BTW I did the gain reduction mod imedeatly after I had played the first songs. I couldn't do more than 2-3 clicks and had some L-R balance problems in that range of the potmeter.
 
After having played around with both OpAmps for at least a week I've come to the following conclusions compared to the original LF:
OPA627: more open midrange, better soundstage and 'smooth' overall character
OPA249: better bass extention and control, much better soundstage and more detailed mids and highs. More forward overall character without sounding harsh (great positioning of Jenifer Warnes and Sara K. 's voices).
The difference in both cases was way more significant than the difference that burning-in made.
 
 
The D1 did not have any problem driving my AKG and Shure head/ear-phones. Plenty of power available. The Stax was an entirely different story. I found out that I have been spoiled by the Wadia 860 that I use to own (I sold it 2 years ago to finance some pro-audio stuff for my studio....) The Stax is the most revealing piece of equipment in my house at this moment. And I found the combination with the D1 in its original shape uninspiring. After the upgrade with the OPA249 it became more acceptable. But I decided to move the Stax to my studio and wait until I've found a real high-end solution for audio streaming to my main system.
 
Still, compared to the Konnekt I'm not entirely convinced. The midrange of the D1 is more fluid and open. The highs on the Konnekt are more detailed, without getting harsh. On the other hand, the D1 provides me with a much better usability for my system in the living room. So, for the time being, I'm a happy user of this DAC/Amp!
 
Albert Jochems