Its sad, I know what you are facing! I have the same problem, the god damned HD Audio (High Definition Audio) is not working with Pinnacle's PCTV application...
Do one thing, set the effect in Audio Settings as "Room" and then you can increase/decrease the volume from the master control!
Anyone else who has a better solution and can make 915GAV work with Pinnacle PCTV Pro, please help us!
Jeet
;(