When I get asked the difference between the 500 and 600, I usually respond the 600 extends 3hz deeper and plays about 3db higher. Both have the same footprint and excellent Axiom sound quality. Assuming your room is closed it measures 1632cf so like Jack said the 500 will be more than enough subwoofer. I would get one 500 now and add a second one for flatter FR in room later.

John