On the topic of the grayscale adapter. I have not examined the schematic in any detail. Does anyone know how the thing works, in broad stroked description?

My uneducated guess is that it substitutes its own signal for the pixel drive (white dot, black dot, gray dot), not sure what that should be called, and somehow synchronizes with the existing screen timing (i.e. the timing for horizontal and vertical scan lines).

So, it would take the pixel "color" from the map in the video RAM on the Xceed board, but would deliver the relevant "pixels" in time with the scan timing already produced by the SE/30's analog board.

But that's a guess...