Check around in Forums whether it supports High Res Audio. Specs on Site can be misleading. My GTX 570 doesnt output High Res Audio. Weird.
You don't really need a sound card if you are going to connect an AVR. The idea is to just passthrough Audio/Video via HDMI to AVR from PC and let the AVR do it's thing.
Check out Assassin's HTPC guide for complete setup.
As far as your budget goes -
40-50K will fetch you Denon + BA or if you can get Pioneer AJ Speakers. These are not my final recommendations just a start, you can be really spoilt for choice.
http://www.hifimart.com/ is a good place to start for Package deals and general pricing info.