ATI/AMD vs nVidia audio processing

I'm building myself a new rig:

CPU: i5 2500K
Cooler: Corsair H80
Memo: G. Skill RipjawsX 1600Mhz 8GB (2x4gb) 8-8-8-24
Mobo: AsRock Z68 Extreme4 Gen3
PSU: Antec High Current Pro 850W
SSD: Crucial M4 128 GB
HDD: 2x Samsung Spinpoint F3 1TB HD103SJ
Case: Cooler Master HAF X 942

I've already bought it all, but I'm not sure about my video card yet, because fps benchmarks aren't enough for me: I plan on hooking it up to my receiver, so I get all 7.1 fine sound from it. I've seen that nVidia video cards can now run 3D on TV's, which is awesome, and by the looks of it, it works better than ATI's...

but what about the audio processing? I've always heard ATI/AMD video cards work very well as audio cards too via HDMI and I was wondering if I'd get the same result with, say, a GTX 580 (tho I'm probably going for a cheaper card to wait for the GTX 6XX series)? Would I get good audio quality from it's HDMI out? Or would I have to buy me a audio card for that purpose?

Thanks!

I'd be most definitely interested in the more high end than GTX 560, from 570 and over... so I guess I'm okay picking eiter nVidia or ATI, right?

Guess I'll try nVidia this time around, my last 4 cards were ATI/AMD.

Thanks a lot!