You can give the S-Video a try w/ an ADB cable. I think I tried this on an 8100/AV and a Wallstreet. IIRC, the video came out greyscale probably because the pinout was different (patch versus crossover or something like that).

I've tried real S-Video connections w/ a DVD player with no results. I think the display is "smart" in that it only allows one video connection and defaults to the composite connection. If there's no composite video signal, then it scans the S-Video. At least, that's my experience. I've never gotten S-Video to work on mine, but I was also never sure I got a good solid connection because the cable I was using had a particulary fat end on it.

Good luck!
Peace,
Drew
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Power to the PowerPC!