windows 7 won't recognize my surround sound speakers and when i try playing music the volume of my 2 rear speakers keeps changing (they get louder and softer uncontrollably.) according to windows all my drivers are up to date. when i go to the playback tab in the sound settings menu, my speakers aren't displayed in the list and when i try to configure the speakers it wont let me choose surround speakers. i tried changing the settings in realtek hd audio manager but still i couldn't select surround speakers. the problem is not my speakers because the surround sound works perfectly with my Xbox 360 and my PS3.
my laptop is an acer aspire 5736z running windows 7 home premium 32 bit
my speakers are Logitech z506 5.1 surround sound speakers