- Enable Surround Sound system (5:1) in Ubuntu

To enable 5:1 surround sound system for your Ubuntu, go to terminal and open the file (/etc/pulse/daemon.conf) using your editor and change the line:

$ sudo gedit /etc/pulse/daemon.conf
; default-sample-channels = 2

to say

default-sample-channels = 6

After you reboot, test your sound using: speaker-test -Dplug:surround51 -c6 -l1 -twav

source:http://linuxpoison.blogspot.com/2010/08/135781677516757.html