Any Intel P55 chipset should support X-fire provided it has the physical slots to accomodate two cards.

I have an Asus Xonar PCI sound card which I use through my funktastic 5.1 headphones, positional audio in games sounds amazing.

But i'm not much of an audiophile so possibly its wasted on me, i just like tech-bling, and boy is my PC bling-tastic! :D