Realtek HD Audio and Surround Sound issues

Apologies if this is going over old ground but I've spent literally hours looking through various forums trying to solve this problem and have been unable to succeed.

I have an HP MediaCenter PC running Windows 7 Home Premium. It has Realtek HD Audio and I have our Yamaha RX-V350 AV receiver connected to the coaxial digial output from the Realtek soundcard. The receiver is DTS and Dolby Pro Logic II compatible.

I can play 5.1 DVDs and surround sound works fine. No problem at all.

However, I now have an MP4 file which MediaInfo, the utility provided with KLite, indicates contains a 6 channel AAC audio. However, no matter what I do I can't convince Windows Media Player 11 or the MediaCenter software to play in 5.1 sound. I get standard 2 channel.

Realtek digital output is set as the default playback device.
In Control Panel, Supported Formats, clicking "test" for both DTS Audio and Dolby Digital correctly results in surround sound being output to the speakers. My receiver actually displays when 5.1 is in use too. DVDs work fine, as indicated above.

I just can't get these MP4 files, encoded in 5.1, to play as 5.1.

I even downloaded some test files from a website encoded in 5.1 in other formats and they too wouldn't play in 5.1, just standard 2 channel.

Is this just a "feature" of the Realtek card or is there something I can do. I've tried KLite codecs and from what limited knowledge I have, couldn't rectify the problem either.

Any assistance, gratefully received.

F

Isn't is possible that the MP4 vids you've downloaded simply don't have the audio tracks to populate all of the channels?

i have the same problem when using klite and its ffdraw filters. i had to use the AC3filer to get surround from any source when i used Realtek. What filter are you using?