hello again,
i am replying to my self. the initial post garnered no responses, so i wrote directly to keith in desparation. he was kind enough to answer and i am posting again to share his wisdom.
if i have understood things, it can be stated simply as r-g-b > s-video > composite. however...
* r-g-b is not the same as y-pb-pr. this may seem obvious, but many products use red, green, and blue rca connectors for a y-pb-pr signal. personally, i i am looking for a hdcp-compliant downscaler and found a y-pb-pr, but not a r-g-b.
* s-video is not officially supported by the scart standard. make sure your receiving device can handle the signal. the bv7-40 can. keith provided me with the pin diagram. i can pass it along if useful
i plan to use a downscaler with s-video + audio output to connect to the bv-7 scart with an appropriate cable. keith indicated that it would be better to use a converter from s-video to r-g-b, but for me this was one box too many.
i hope this helps any one else with similar questions. and thanks again to keith !
- scott