In Addition/Response to the comments about Motion Sound amps in the other thread: My keyboard player plays through one, and it sounds excellent. The build quality is very good, and it really does capture that Leslie sound in a much, much smaller package.
The low end is nice and solid at moderate volumes, and I can't see any reason why you couldn't run a bass through it, though the output would be very low, and it'd have to be mic'd.
Cheers!
Rob