I suggest adding to a section to the Volume Control GUI, to make configuring surround sound easy.
The section should include:
- a picture of each speaker setup, to help the user know which setup they use.
- a button to test the speaker setup, similar to the Sound Preferences window.
- a button to access advanced speaker settings, such as Rodrigo's options (see Solution #2)
An example, is how Windows 7 configures surround sound: