Asus P4PE - Manual (Page 126)

5-22 Chapter 5: Software support
4. To change to 6-channel speaker setup,
click the arrow to display the options.
Select 5.1 surround sound
speakers, then click OK.
5. Reboot the system to effect the
changes.
Adjusting the volume settings
1. After rebooting the system, click on the volume control icon on the
taskbar (lower right corner of your desktop) to display the Volume
Control panel.
Volume control icon
2. If you installed an S/PDIF module,
click on the Volume Control Advanced
button from the Volume Control panel.
The Advanced Controls for Volume
Control window appears.
To achieve 6-channel audio capability
when playing DVDs, check the boxes
opposite AC3 SPDIF and PCM SPDIF.
Click Close.
You do not need to do step 2 if you did not install an S/PDIF module.
Your new settings take effect only after
you reboot.