Shoutbox

You can only get 5.1 with an optical cable. So get an optical cable and plug it into your 360's a/v cable and then into the 5.1 and use the other 5.1 cables to go into your PC's sound card that supports 5.1.

or

You can use all 5.1 speakers on your 360 but it will only be stereo sound by converting the 360's stereo L/R to 3.5mm female and then plugging it into your 5.1's 3.5mm jack (usually green).

Another way to get only stereo sound via your pc is to plug in your converted stereo=>3.5mm into the PC's 'line in' which will route the sound back out through your PCs audio system.