Vista Media Center/HDTV issue

Hey everyone. I have just encountered what I believe is a vista media center issue, but i am sure there is something i am doing wrong. I recently installed a sapphire radeon 4650 in my gateway sx2800 slimline machine. I purchased it to hook my 42"LCD hdtv to my computer for video watching. I originally installed it, and installed all the latest drivers while running windows 7. However while running win 7 all i got when i hooked my hp 24" monitor to the dvi and the hdtv into the hdmi port... the screens are just black. However the hp worked fine until i plugged in the hdtv. so i thought maybe its a win 7 issue. So i went back to vista...installed all drivers and plugged them in and hurray it worked perfect. or so i thought. everything is fine, except when i play a divx/avi file or mkv file in vmc and use the hdmi out sound for my tv.. the sound is really low. i have turn the volume almost all the way up to 100 on the tv just to hear it. I had to switch back and use my computer surround sound speakers just to watch a movie last night. however, when i ran the video using divx player, the hdmi volume through the tv is fine. which is why im sure its a vmc issue. This is what I have installed. I have media control 6.0.2 64 bit so i can play divx/mkv files in vcm. fddshow revision 3096, divx codec, and ac3 filter 1.63b. could any of that be the problem? Thanks in advance for the help.