By default; Windows always sets the speaker configuration to 2 speakers (or Stereo), so in order to setup a 5.1 speaker system you will need to go through the Control Panel.
Start-->Control Panel-->Hardware and Sound-->Sound-->Configure-->choose your configuration
Just follow the steps, click " Apply " , then Okay.
You may also have to set the audio in the BIOS to HDMI
Hope this helps
Is there anyway to get my HDMI audio pass-through to be in 5.1 surround sound? I currently have audio coming out of my system but it's only in 2 speakers. If you need more system information just ask.
Mobo: Asus P5Q-SE2
GPU: Nvidia Geforce 9600gt