When I looked into this I was told by the OPPO support folks that they use 12-bit/108Mhz video DACs for s-video. The s-video on all the models is the same. BTW, s-video is much, much better than composite. With a good cable the luma (monochorome) sharpness is not real different from component at 480i. The chroma channels suffer at higher frequencies, but depending your TV and eyes you may or may not notice much difference. Since this is only 480i you need not concern yourself with having the fanciest DACs as I think PooperScooper indicated.
I found a great comparison on this page:Comparison of video signal quality
I would be interested in hearing from anybody who has evaluated the PQ of the OPPO players with 480i from either s-video (any OPPO) or component (970 only). I have played with a spare, cheapo Pioneer DV-393 player which hapens to use the same Mediatek MPEG decoder as the OPPO and the image over s-video is not bad on my 38" direct view Loewe Aconda CRT. I would expect the OPPO to be better, but don;t know for sure.