I have a Gigabyte Z170MX - Gaming 5 motherboard with Logitech Z-906 speakers connected. I turned off my desktop one evening, and the next day my 5.1 surround had suddenly decided to stop working. It is only playing in 2.0. No Windows 10 (x64) updates were installed, and none of the drivers got updated. All drivers are up to date, and so is my Windows. Both Realtek HD Audio Manager and Sound Blaster X-Fi MB3 say that my surround speakers are connected, although testing or actually playing games/videos only plays sound through my front left and front right speakers. I have gone through all the configurations and settings I can think of to make sure it is all set to 5.1 (which it is), and uninstalled/reinstalled drivers over and over. All the cables for my speakers have been replaced (making no difference), and all cables are properly connected.
The weird thing is it was working properly when I was using my desktop (for about 10 minutes) yesterday. But now it is back to 2.0.
Games and videos TRY to play sound through my other speakers, but ends up being mute.