I cannot comment on the 'rex' processes not having used them. It just seems strange to me that they would pick up speed beyond the UV range. I don't dispute it, but if I ever get to doing it, I have a spectrosensitometer to test the materials with to see what is going on.
As for Selenium and Cadmium, I think that Se will be just fine as a material to generate electricity from sunlight and Cd due to toxicity is safely left on the shelf. But, there is quite a gem of truth in your comments about these two elements.
After all, if cuprous oxide works, what else is out there. I think that the field is open for a good investigator and suggest that you look for the book by Khosar or Kosar, I forget the spelling OTOMH. Fascinating book on alternative processes. I have read it cover to cover and unfortunately have forgotten most of it due to disuse and time. Everyone wanted Ag emulsions and not these 'old fashioned' dinosaurs. (well, now here we are with 'rex')
Best of luck with your trials, I'm working with cyanotypes myself right now, trying to tweak some things.