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:
![alt text](../../I/static/images/5b8eda6ad6bd74999cc6affdc5bd631c2a3f678839ef17dd96744d77bb71c08e.jpg)
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.
![Fill speakers](../../I/static/images/2940eb644d79a591cc2cc74534d7dcf0518feb7f4c7ce837176d83cc0a61071e.jpg)