the 360 has a optical out , if you look on the back of the av plug at the xbox end i think the output is on there mate , then just have a look on the connections on the surround sound for a simular connection , turn on the surround sound system when youare looking for it it will shine red this is the optical laser
http://www.avforums.com/forums/xbox-360/508419-optical-output-xbox-360-a.html have a look on here