Some of them (mostly from the latter two categories) are capable of high quality playback of two-channel audio, however I have yet to come across one for which that was the primary design goal. I have found sound cards for gamers, sound cards for home theatre users, sound cards for amateur musicians and sound cards for professional musicians/recording engineers.

There really aren't any 'audiophile' sound cards, at least not that I have come across on my travels.

I agree with CharlyD but here are a couple of aditional reflections:

What if one is using only the digital stream (say coax digital out) from an internal sound card: do noise issues of the PC have any effect? What do you think of this? Isn't there also the issue of the quality of the DAC in the sound card? Even if true, wouldn't the best sound come from the card with the best DAC, either internal or external? You simple won't introduce noise on recording with these cards. The converters in our M-Audio sound cards probably better than in any of your other audio gear. It is simply more convenient to work with and given the quality of the shielding on the sound cards we sell, there is no advantage from a noise standpoint. In fact, given the choice, we'd always choose an internal sound card over an external for a desktop machine. This simply isn't true for professional sound cards. Many folks choose USB or Firewire soundcards for their desktop PCs because they believe that old adage that processing audio outside the machine is better. See then this quote from Tracer Technologies, who market both kinds of cards:

Why? Because of the inherent noisiness of PC's. I've long assumed a good quality usb sound card would deliver better sound than an internal PC sound card, even of the audiophile variety.

Best external sound card for audiophile