I would choose a sound card with the lowest THD% or Total Harmonic Distortion if you can find the specs. Also choose a sound card with a high SNR (signal to noise ratio) and you should be pretty happy with the card, Then make sure to use some extra ferrite on the audio lines to help keep any extra rf type of noise out, and you could go pretty extreme with some shielded audio cables. I have had 5 cards now and the only one I have been happy with was the Turtle Beach Santa Cruz which used a crystal chip set. It was a super clean card and low priced but, they do not support it anymore I can not run it on windows 7
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