Well I dont actually have one but its looking like a digital 'optical' cable is what ur after
http://www.xbox.com/en-US/support/systemsetup/xbox360/console/digitalaudio.htm
You can use the phono outputs that are attached to the video cable. Alternatively (as i'm guessing your using a hi-fi amp not a AV receiver) you will have to use the optical cable running it through a DAC or something.
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