If you have no connections beyond the red/white (left/right) analog audio output, then that's what you want to use. You can run that and the composite video (the yellow connector) to a video input on the 970 and then set up that input of the 970 for analog audio and composite video. As loopy mentions, you can use Dolby Pro Logic II to get surround sound. Since you have digital cable, though, you might think about asking about swapping the box for one that offers a digital audio output. You should be able to simply stop by a Comcast office and trade with them, no service call required.