1) If the Windows test is working it should be setup properly.
2) You should also use the software for your audio solution (if onboard that's likely Realtek HD software from realtek. It's also from motherboard site but Realtek site is usually up to date).
http
/www.realtek.com.tw/
You probably need the file with THESE DETAILS (can't link directly likely): R2.76 2015/4/21 113999k
3) Are you SURE it's not really surround? There are plenty of programs that it's hard to tell.
Do you mean that the REAR SPEAKERS have no sound, or have only the EXACT same sound as the front speakers?
Summary:
Again though, in my experience, if Windows "Playback Devices" are correctly demonstrating all speakers working then you're setup correctly. Perhaps you need to look at more software/games or even find examples in the Realtek (or sound card) software that can demonstrate surround mode is working.