It's not an easy size rout to fill. I had a Fortress Masterman and tried to change it out, but it wasn't easy. FWIW, I put an EMG 35 sized pickup in with a chunk of wood to keep the space filled.
Delano does make a pickup in that shape.
I do agree that the electronics are lacking. Mine had one of the bass/treble stacks just... die.
Are you opposed to using a different preamp to change the tone?