I have problem with Realtek 5.1 driver for Windows 7 x64. I've installed newest drivers for Realtek HD Audio, but 5.1 still doesn't work, the only thing that works is front stereo. However, when I click on single speaker in sound settings test, every one of them work.
I never got surround sound working perfectly in Windows; the only solution that has ever worked was switching operating systems. I now have Ubuntu and enjoying perfect 5.1 sound now, all my boxes are working.
However I think I managed to get the Realtek high definition audio codecs working in Windows 7 though. But there was a lot of struggling. I had to search a long time till I actually got the Realtek audio interface, this one:
Just go to this link: http://www.realtek.com.tw/downloads/
Install the audio codecs, after the reboot, go to your configuration screen, choose sound, and the audio manager should be integrated in a new menu there. I'm not sure about this.
In the speaker tab, you have to check "Speaker fill" to enable the rear speakers.
I believe that the application you're using must be sending 5.1 audio for it to work.
You can't just play a 2.1 source and expect it to be replicated on all channels.. 5.1 expects a different track for each channel.
The RealTek UI is really crappy though, and it should have an option to replicate the audio onto all channels, but it seems you have to use a plug in for that.