Analog signal inside a computer box is a bad idea. I don't think there are any audiophile quality internal sound cards made now. Card-D was good, but now defunct. Lynx22 is good for the money, but it is intended as pro audio card built to a price, with opamps and surface mount caps galore, not to mention D-sub output connectors.
On the other hand many high end audio companies have developed USB DACs which offer extreme performance and refinement. Ayre QB-9, Wadia 121, Antelope Zodiac, Sim Neo380, exaSound E20, these are among the best digital conversion available, all use USB to connect to a computer.
There is still plenty of crap for sale in USB "audiophile" DACs. Older USB 1.1 and some 2.0 DACs were/are still limited in bitrate and jitter rejection, but the newer batch in the last couple years has solved those issues, and they cover a wide price and performance range. Look for "asynchronous" to describe the newer variety, or look for sample rate via USB over 24/96.