Let me start by saying I am having the same issue since upgrading to windows 7.
I currently have an p7p55d deluxe mobo and was using realtek onboard sound with logitech x-530 5.1 sound system with win7. Before this I had winXP and when I use to play mp3's/videos/watch things online, the rear speakers would give off a surround sound feel. I suspect this is the 'speaker fill' function or something similar to that nature.
However since upgrading to windows 7, I have noticed that my rear speakers are pretty much useless and I can't seem to enable/replicate this ability
I have since purchased the aforementioned Auzentech x-plosion in hopes that this may help solve my problem. As it turns out, I'm having more trouble just setting it to 5.1 as the card wont read my rear speakers in the jack. I can only get sound to go to them when i change settings to 7.1 instead.
Ultimately what I would like is a solution to get Speaker Fill workign on windows 7. I have no clue if this is a win7 issue, driver issue, or speaker issue.
If anyone has some advice out there i'd be really grateful! =( I really miss hearing something in my rear speakers
Disable Azalia(onboard) in your bios.
Download and install Driversweeper it's free.
Run in safemode
Check off Realtek
If that doesn't work you'll have to play more with the C-media interface.
Just installed an X-Plosion card on a WIN7 64bit 5.1 set-up works fine.