It will be interesting to see and read about your findings. The sphere might be a bit of a task though, and if I were in your situation, I’d try to see what I get with light directed to a projection screen and use that as a backlight. That should work…if your setup holds the negative like a Nikon ES-2 to prevent stray light…which is not the case now, if you’re still using the setup you described in this post: