I can tell you that several of Sonic 3's tracks will straight up lock up the Genesis when you played through the XGM player. So I'm assuming that is partly what you are talking about? Tracks that I've not been able to get to play through XGM are Ice Cap Zone 1, Blue Spheres bonus stage and one other that escapes me at the moment.
Also, Stef's compilations have the game logos on them. It would be cool if that could be incorporated into the XGM rom builder somehow? As long as we know the format for the graphics etc. It would be very cool to have that.

