In reply to:

We ran a spare coax so I guess worst case we could run the OSD across composite

Even then, I don't think most send over composite... you'd have to use the S-vid out, with a s-vid to composite adapter (or just tie the luma and chroma lines together on a 4 pin connector, the 7 pin connector already carries composite on one of the inner pins - all these lines already carry the sync so no worries there!)

Bren R.