What's the best USB audio interface?

I want to set up a dedicated music server on an old book-sized PC, digital out to an outboard DAC (a cal Gamma, but it could just as well later be another DAC) and then onwards through a headphone amp to cans.

So the PC will serve as the digital source or occasionally as a CD transport. There won't be any recording/input needs - and USB will be the way to go to bypass the onboard sound card (no free PCI slots anyways).

In searching for a suitable USB audio interface for this purpose, I've run across references to M-Audio/Midiman (sonica and others), Roland/Edirol UA 30 (or 3(D)), Xitel, Ego-Sys, Audiotrak - many more... the market seems to be moving fast ... I'm lost in the thickets.

I'm not looking for a one-off solution, consensus of any sort, nor do I expect to get great sound w/o a proper transport, better DAC etc. I'd be grateful if any a-goners could share their relevant experience (success? trials & tribulations?).

Take a look at another Edirol product, the UA-1D. It's just a simple USB in/out with both coax and optical connections available (only one at a time). Hope this helps.
This is what I use stereo-link.com, USB dac with head phone and rca outs.
The M-Audio sonica seems like a good choice. It's just like the Edirol, apparently, in that it has one coax and one toslink output. M-Audio makes good stuff, but I haven't used the sonica before. Considering the source material, I'd go for whicherver one is most affordable.

We use and sell the Ego-Sys. I can verify that it is a very very good product.
Apogee Digital just released the Mini-DAC, which offers USB audio input/output along with other various i/o options. More than likely overkill for what you want to do, but an option to consider

The Edirol UA-1A will do the job for you,
doing the D/A conversion as well.
But the UA-1D passes SPDiF/Toslink
to your DAC and I'll bet your DAC is
better than the one in the UA-1A.
Go for the UA-1D.
Interim Summary.

Thanks to all the a-goners who have breathed life into this
thread. Your input has been very helpful and is certainly greatly appreciated.

Some URL's for quick reference
(for anyone who is, as I was, totally lost):

One user's experience with the Roland UA-1D

Successor? of the UA 30, UA 3D

Motu 828 is an (expensive) USB audio interface

A short review of the Roland / Edirol UA 30

Audiotrak (EgoSys) OPTOPlay, simple feature-set similar to the UA-1D
Maya 7.1 USB (overkill) -- http://www.audiotrak.net/eng/maya71u.html

ESI U24 waveterminal (esi-pro.com, ESI=formerly Ego Systems or EgoSys)
http://www.homerecordingmag.com/review3.asp (truncated review)

Ballpark price points:
USD 0.1k - Sonica; UA-1D; Optoplay;
0.15k - UA 30, used; Stereo-Link 1200 ($169: 220-240V internat'l version);
0.25k - ESI U24 Waveterminal;
0.8k - Motu 828 (firewire 2xXLR or 1/8" to RCA);
1k+ - Apogee Mini-DAC (shipped Mar2003, price est. mini-me based);

Possible strategies:
- kiss (keep it simple,stupid): Optoplay; UA-1D; Sonica;
- added flexibility: UA 30; UA 3D;
- better build: ESI U24 waveterminal;
- consumer convenience: stereo-link;
- overkill: 828; mini-dac;

For the moment it seems that the k.i.s.s. strategy wd be most reasonable. Information/3rd party reviews/tests on the ESI/Egosys/Audiotrak products is harder to locate (they've got good mentions elsewhere in the forums tho). There are some unresolved issues: e.g. compatibility with the OS. Ultimately, I'd like to get this setup running under some flavor/color of Unix -- Linux or a version of BSD -- with a low-key text-based GUI (vs. some color and graphics-intensive one in windows) controlling the whole thing. There is some learning curve. The contributions are encouraging.
I have the M-Audio Sonica. I like it a lot. It runs to a Monarchy DIP and then a ART DI/O DAC and then to my preamp. Music sounds good.

The Sonica requires Windows XP or 2000.

The m-audio description of the sonica mentions Win XP, 2000 but also Apple's OS X. But I wonder whether the sonica might still work with linux kernel 2.4 and above which has USB support - OS X is Unix-based as far as I know. I think it may be to some degree widespread that USB devices can be used with Un*x, even if this OS is not officially supported. May be just wishful thinking tho.
I am using an older computer as my music server. I am currently using a AMD K6 522 mHZ CPU with 256 MB SDRAM to host about 4000 mp3s (legal downloads from www.emusic.com) and a bunch of live shows in the lossless SHN format. I have several older used hard drives and a PCI IDE controller card which controls the three hard drives and the one CD-ROM (a generic Creative 24x). The computer is also networked to a faster CPU with even more music (more SHN files). I have a generic 2 MB video card. My OS is WinXP Pro. I don't have any other hardware (no PCI soundcard or modem). This computer is basically a bunch of old parts that I had laying around.

My media player is Foobar which uses the kernel streaming to move the music out the USB port. Foobar sounds much better than the other media players I have tried (WinAmp, FreeAmp, MusicMatch, MS Media Player) and uses far less resources. It only works with the XP/NT. Foobar also has fewer features than most media players. It is a slim player and not full of bloat like many of the others.

Attached is a review of the Sonica from ExtremeTech:

Also, I have not found drivers for the Sonica except for NT/XP drivers.

Hope this helps.

Definitely helpful. Foobar sounds interesting, on the order of 0.5mb of code - small and has a v. active developer community going for it; merits closer inspection.

I just read that the Xitel Hi-Fi link only needs USB drivers--no hardware specific drivers. It should work fine with just about any OS.
Never mind. The Xitel has it's own DAC.
the ua-30 seems nice because you can directly plug in a guitar and record.. can anyone who owns this comment on its playback? would it be better to use the rca jacks directly to your preamp or a use the digital cable and run it to a separate dac?