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?).

Thanks,
agonanon
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.

http://foobar2000.hydrogenaudio.org/
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.
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?