yea, get an ATI 5xxx series VGA will do the job for both HD video and audio

HD 5850 spec :

Integrated HD audio controller

* Output protected high bit rate 7.1 channel surround sound over HDMI with no additional cables required
* Supports AC-3, AAC, Dolby TrueHD and DTS Master Audio formats



however, of cos you still need a HDMI AVR as well haha...

advantage HTPC to PS3, i guess its just reading extra video format in softcopy way (mkv, m2ts, bdiso)