I want to be able to get 5.1 sound from my Xbox. My receiver was already prewired to my plasma TV with component video cable as part of the home building process. I have the Denon 1708 receiver. I know that I can't go into the Denon with HDMI since this will mess up the video (as it is component video out to the TV). Is there a cable that would allow me to go in to the Denon with component video and an optical cable for audio? I can't seem to find this cable (if it exists).