Problems getting MP4 to play in 5.1 using WMC

Hello-

I seem to be having difficulty getting Windows Media Center (Windows 7) to play my converted .mp4 videos using all 5.1 channels.

I am converting the video from DVD using an up-to-date version of DVDFab9. The video is converted using the H264 codec. The Audio has been tried using both the AAC and the AC-3 codec. The MediaInfo utility has confirmed that the .mp4s created contain 5.1 channels of audio.

I have installed the Shark007 codec management utility on my HTPC. Using both the Windows default settings and the Shark007 recommended settings, I get the same results.

My HTPC uses a Creative Labs SoundBlaster X-Fi Xtreme Audio soundcard with up-to-date drivers, connected to a Yamaha 5.1 channel receiver via an optical TOS-Link cable. The main method I am relying on to verify that all six channels are playing is to look to the channel indicator LEDs on the display of the receiver.

These are the results I get:
- If I have DVDFab9 simply copy the entire contents of the DVD to a folder and tell Windows Media Center to play the DVD folder contents, the audio plays using 5.1 channels.
- If I have DVDFab9 convert the DVD to .mp4 (using the H264 video and either the AAC or AC-3 audio codecs, as mentioned before) and tell Windows Media Center to play that file, the audio plays in 2 channels. Again, as I mentioned before, I am verifying the presence of all six channels in the converted file using the MediaInfo utility and relying on the receiver's display to verify that the channels are (or aren't) playing.

At this point, I'm unsure of what to try next. I would appreciate any suggestions.

Thanks!
SRD