That setup will make a nice gaming HTPC. As for the sound, will you be running a receiver?
There really isn't a "conversion" from a gaming PC to a HTPC, the main difference is if you use media software like XBMC, etc..
Equipment - 60" Vizio M60-C3 - Denon AVR-2300W - Pioneer BDP-150 - HTPC, Xbox One - Sennheiser RS170 Headphones - APC C25B Power Filter
Speakers - SVS Prime Center, Bookshelves, Satellites, Dual BIC F12 12" Subs
HTPC - Intel Core i3-3220, 8GB DDR3 1600, 750ti 2GB, 7TB of HDD's, LG Bluray