Elite Bastards posted a review on the ASUS Xonar DS PCI sound card

Compared to the larger PCBs, complete with EMI shield, that we're used to seeing from ASUS' Xonar parts, the Xonar DS is certainly diminutive, doubtless taking some hints from the small form factor of Auzentech's X-Fi Forte which proved that audio quality needn't be compromised by using a small physical PCB. Also of note here is that the OPAMPs used by the Xonar DS can be replaced by the user if you're looking for even higher quality analogue audio output.

ASUS Xonar DS PCI sound card review