Hi Tom,
I just posted a redrawn diagram to get a better overview of the effects order. Since, for some reason, the resolution is reduced after the file transfer, I put a copy here too :
http://joachim.milson.free.fr/cs80-interactive-diagram/CS80-effects.jpgWhat you're trying to do was originally planned by Yamaha. It is visible on page 66 of the Service Manual, where the WAH alone is drawn but was carefully struck out.
On the next diagram, I have reconstructed what the initial design might have been :
http://joachim.milson.free.fr/cs80-interactive-diagram/hypothetical-initial-exp-wah-design.jpgNote that this only an hypothesis and I do not pretend that it works. Anyway, that gives the idea. The reason why Yamaha chose not to do it is not clear. Perhaps the PRA board was already full ?
As for controlling the brilliance, that would require an other design.
Joachim