Hey guys,
I just registered here to share my experience.
I have a Creative Audigy 4 in my system as well as the Realtek ALC888 onboard. I used to use my audigy before Windows 7, but Creative has still not released properly working drivers so I switched to my ALC888. Initially I was using the drivers from MSI's website for the Realtek, and all was fine. When I tested the speakers in the control panel and Realtek's control panel, every speaker output sound properly. While listening to music today, however, I noticed my rear/center speakers were not outputting sound. I updated my drivers to the 2.40 from Realtek's site, but no dice. I can still get sound from every speaker when I test it in the control panel, but not when playing music. I spent the last 2 hours fiddling with settings, but nothing worked. After reading the post on here about sound playing properly in games, I started up CS:S just to test everything, and voila: all the speakers are working. However, I still only have stereo sound when using WMP and foobar2000.
Hopefully my experience will help someone pinpoint exactly what the cause is.
On a side note, I am able to get sound from the rear/center if I use speaker fill, but we all know how crappy that sound quality is.
*Edit: Ok, so I decided to update my audigy drivers with the latest beta from Daniel K to see if I would have any luck, but I have the same issue that I have with the Realtek (in addition to other problems the audigy has that are unrelated). I'm thinking this problem has got to be related to a Windows 7 setting instead of caused strictly by the drivers.