I didn't have any luck bypassing the box and jumping power to the motor. It would spin once or twice then shudder back and forth while trying to cook the wires. I never did cut the wires to eliminate the box on the old style motor I played with. Maybe eliminating feedback from the control box will help.

When the fan died, would it start again?
How long did it run on 20 amps?

I see that your fan is an aftermarket unit also. I wonder if it's made by the same people as the one Performance Only used? Is there a manufacturer's name on the motor or controller?