upgraded HTPC to Win Vista x64 now I get no audio playback on OTA Digital channels!

using the following:

using Windows Vista Media Center

sound: ABIT IP35 Pro onboard: realtek HD audio w/ optical audio out (this is setup to play out to my home theater receiver, it plays MP3 and games just fine, aswell as analog cable, ad ssues when I was setp on Windows XP)

tuners: hauppage hvr 1600

You might want to check the Vista sound mixer to see if something is muted.
also, check hauppauge website for vista 64 driver updates.
The included driver might have an issue.