Hi
I have 7 x64, whenever i play mp4 files with multichannel AAC audio track my AMP only shows 2 channels. I know this happens because amp usually cannot decode AAC, but i had this problem before and it was fixed by tweaking something. I dont remember now as i reinstalled since then.
In MP Video Codecs settings, under AAC audio decoder i have 5 options MPC/MPA, MPC Real Audio, MONOGRAM, ffdshow and MS DTV/DVD. And under MPEG/AC3 audio i have 4 options - MPC/MPA, MS DTV/DVD, AC3 Filter and ffdshow.
Digital COAX is in use to connect my AMP to HTPC.