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,