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).

Are all digital outs (USB or otherwise) thet produce 24bit the same quality? Would something like the new Creative X-Fi give me a better quality digital out then one of the externals that you recommended, or all they all the same?

Sorry, don't know much about things at this level...

Try both connections to the outboard reciever and let your ears determine what sounds best to you! It still does not matter what you use to feed the bits to the DAC. USB or sound card will not matter in the digital realm with 44.1khz output. Most Creative cards will not output 44.1 SPDIF. The Burr Brown DAC is a excellent D/A converter. Bits is Bits no matter what you use. The DAC is where the sound quality comes into play.

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.

"Bits is Bits no matter what you use."
I'm a little confused by this. Is jitter no longer an issue when the data source is a PC hard drive?