I'm running Windows 7 Media Center and playing mp4 videos. The sound is being output through an HDMI cable. The videos are encoded in 5.1 channel sound but when I play them in WMC the sound only comes out in stereo and not 5.1. Other forms of media come out in 5.1 (e.g. tv tuner signals, DVDs) so the problem is definitely the playback of that type of file. I can't seem to find a setting to change that or update it. Any help is appreciated!