Best soundcard if have outboard DAC

I would recommend skipping the soundcard--get a USB audio output device like the Waveterminal U24 that will output spdif. Other cheaper alternatives include the Edirol UA-1D or the M-Audio Sonica. If you use USB instead of coax or optical, it sounds better for longer runs. You will still need a short coax or optical to connect to your receiver (the general consensus seems to be that coax is better, but there are some situations where people claim the optical is superior--you would have to try it).

A lot of computer devices output at 48 kHz, not the native 44.1 kHz for ripped CDs. I know the waveterminal outputs 44.1. Bits are bits, but certain device may be more prone to jitter problems if they have lousy cheapo clocks in them.