Bit-Tech published a review of the Asus Xonar D2 Soundcard

Asus is onto a winner in some respects - the bundle is the best we've seen to date, the card is made extremely well and includes some awesome features. However, these features are still identical to the CMedia Oxygen chipset we've been looking at for nearly the last year now. The software included has potential, but it's the usual "looks good and sacrifices ease of use" and the drivers in Vista still need some work, but its certainly better than the CMedia Oxygen drivers (although not its software). If you were a hardcore gaming nut, you still wouldn't buy this over an X-Fi - that's a given, but for the casual to regular gamer it will still suffice and with more and more games including Dolby features over EAX, like Bioshock for example, both cards should offer an equal temptation.

Asus Xonar D2 Review