Go for a Creative XI-FI based sound card. Honestly Asus are just using C-MEDIA chips in their cards. The C-MEDIA haven't produced any new chip yet recently, the ones out their are PCI based. so the Asus cards has to convert PCI back to PCI-E so its pointless you go with a ASUS PCI-E sound card.
If you can spend few more then go for a CREATIVE CORE-3D thats truly a wonderful sound card.