USB to SPDIF converters shoot-out : EMU 0404 USB vs. Musiland Monitor 01 USD vs. Teralink-x vs. M2Tech hiFace
__Teralink-X :__
The Teralink is the easiest to use. It doesn't need custom drivers and works with Direct Sound and ASIO (through ASIO4ALL).
It has I2S, BNC, Spdif and optical out. This one is a "plug and play" unit that performs flawlessly but is limited to 16/44 and 16/48.
It is possible to install custom drivers (thread here) but there are no sonic benefits in doing it (those drivers introduce many additional processing to the sound which I found to cause a degradation to the sound in my opinion).
__M2Tech hiFace :__
The M2Tech hiFace is a very minimalistic unit : it has only one output (I ordered mine with a BNC output) and it plugs directly into a usb receptacle without the need of a usb cable. For now, it has only drivers that work with Kernel Stream and it works with Foobar, Media Monkey and WinAmp.
DS and ASIO drivers are expected later down the road.
The unit does 24/192.
__Sound :__
__Musiland Monitor 01 USD :__
The Musiland Monitor 01 USD is a definite step up in sound quality compared to the EMU 0404 USB (and incedently compared with the usb input of the dac-19mk3).
The highs are cleaner and the bass tighter. The soundstage is a little bigger and there is better separation of the instruments.
Finally, while it is not harsh sounding like the EMU 0404 usb, it lacks some of the sparkle and life that the better converters (teralink, hiface) seem to inject to music. It is not bad by itself but the music seems to be constrained and tight once it is compared with better units.
__Teralink-X :__
When I bought the Teralink-X, I was not expecting much from it. At that time, I already had the Musiland unit and I was just curious to see how it performs because it uses high grade capacitors and a low jitter clock.
Straight out of the box it performed very well. After a few days of burn-in, the sound improved dramatically and it outperformed the Musiland unit easily.
The bass got deeper and more powerful, and the highs became more extended and sweeter at the same time. It is like lighting up a picture and discovering hidden details. But best off all, that increase in overall resolution did not increased the "edginess" of the sound. In fact, the sound became smoother.
The soundstage became bigger, almost limitless. In fact, on most recording I don't feel that I am listening to headphones, the only thing that keeps reminding that I am listening through headphones is the pressure of thesennheiser hd-650 on my head.
The imaging is precise, and hollographic in many recordings thanks to the precise separation of instruments and voices. Every instrument/singer has its own place on the soundstage.
Overall, I find the sound sometimes too good to be true. I got accustomed that only a few "audiophile" recordings sounded great in my system, however with theTeralink -X all recordings sound enjoyable in my system. I can still hear big differences between quality of recordings, the encoding used (mp3,flac, wav), but the Teralink-x, especially when paired with the Belden BNC cable, lets you focus on the positive sides of the recordings which is some might call "musicality".
Note on digital cables :
The Teralink-X works best in my system with the Belden BNC cable.
When paired with the Belden cable it gives a wide soundstage and a very smooth sound, "tubey like".
When paired with the Hifi Cables Sobek BNC cable, I get an increase in resolution, but a smaller soundstage and an increase in brightness "edginess".
Note on burn-in :
The Teralink-X needs a few days to sound its best. It doesn't sound bad at first but after a dew days of continuous play-back, the sound opened up and the bass got deeper. TheTeralink -X uses many capacitors inside that might explain the big change in sound that I did not notice to that extent (or at all) with the other converters
__M2Tech Hiface :__
The m2tech hiface is my newest usb to spdif converter, I have only owned it for a few days, but I have listened to it for enough hours now to get a sense of how it sounds. This minuscule unit is simply outstanding.
First, the music just makes more sense. The notes flow more easily and it requires less efforts from the listener to understand what the performers were trying to convey. There is also a general increase in resolution that makes the music more real, probably because of its better retrieval of low level information on the recordings which makes reverbs and ambiance hall more audible in Live recordings and Classical music.
Second, the soundstaging is wonderful. It has a better pinpoint and 3D imaging than the other units, and there is a even better separation of instruments and voices. In fact, whether it is because of better imaging or because of better dynamics, the result is that instruments and voices seem to have more acoustic power (while playing at the same volume levels as I did with the other converters), the presence factor of performers and instruments is much higher.
Also, while the soundstage with the Teralink-X is big, there is not as much differentiation between recordings. With the hiface, the soundstage changes a lot (in width, depth and height) between different recordings.
Finally, the frequency extremes seem to have been extended with a more shimmering and extended highs and more articulate and tuneful bass. Compared to theTeralink -X, there is also a shift in the tonal balance to a more neutral and faithful balance. There is a better differentiation between the quality of the recordings and it doesn't impose a sound signature on the recordings : Warm recordings come out as such and over-processed recordings are highlighted as such but are still enjoyable to listen to.
Final note on the Hiface :
Each time I was doing A/B comparisons with one of the other units, I would end up listening to the M2tech and forget about my review. Unplugging it to put another converter was a tough experience each time because I had to be pulled out of the music.
Beyond the criteria I described above (soundstage, resolution, ...), the M2TECH hiface was the most satisfying unit from a sonic point of view as it was the closest to real representation and offered the most believable representation of music.
__Conclusion :__
Getting a clean spdif signal from a usb port of a computer seems like a simple task but appears to be a rather complicated endeavour. There are many usb to spdif converters today in the market and it is hard to predict how they perform. Their performance is tied both by the quality of the drivers and the quality of the components (clocks,spdif transmitters, ...)
Out of the 4 converters I tested in my system, the m2tech hiface is the one that did the best job. I have indeed been very impressed by the performance this extremely small unit and it doesn't even require a usb cable. The designer of the hiface paid great attention not only to the proprietary drivers (like EMU and Musiland) but also to the quality of components and clocks that are used.
Granted it is the less flexible unit to use as it is limited for now to KS (Kernel Streaming) with limited media players but its superior sound quality makes you forget about its limitations.
The Teralink is the second best performing unit that is leaning a little bit on the "warm" side. However, it was only when I listened to theHiface converter that I became of that coloration.
If your library contains only CD files and mp3s, the Teralink-X is very good as it combines both a "high resolution" sound with a slight warmth that makes it more forgiving toward less than perfect recordings.
However, when you add the cost of a high quality usb cable, the overall cost exceeds that of the m2tech hiface. So it is hard to recommend it because it is limited to 16/48 and doesn't sound as good as the m2tech. Any "audiophile" who is willing to buy such a converter would likely either purchase theMusiland for its convenience or the m2tech for its performance.
The EMU 0404 usb comes last (old drivers, components of average quality, and requires a high quality usb cable). However, it is the only unit that has analog inputs and outputs. In my opinion, it should not be bought to serve only as a USB to Spdif converter. There are many units out there that are cheaper and that perform better.
__Jitter measurements:__
While jitter measurements should be interpreted with great care (different results with different equipment and test protocol), it is sometimes a nice tool to make jitter comparisons in the same group of transports done with the same equipment.
Here you can find jitter measurements of the m2tech, a LynxTwo pci sound card, a Nagra DII and a Marantz CD player. In that test the m2tech was slightly better than the LynxTwo which is a professional grade PCI card, and better than the Nagra and Marantz cd player.
On a stereophile test, there were measurements of the EMU 0404 usb and other converters. The EMU had the worst jitter of the bench, and its jitter was 8 times that of the one measured with the m2tech (Granted the tests were done with different measuring equipment).
So, it seems that at least, I must have gotten the order of those 2 units right 
http://www.head-fi.org/forums/f7/usb-spdif-converters-shoot-out-emu-0404-usb-vs-musiland-monitor-01-usd-vs-teralink-x-vs-m2tech-hiface-449885/
