What are you trying to accomplish with the multiple subs? You will fill the space with PLENTY of bass from a single decent 12" sub. End goals are a much to know here.

Do you just want louder with some peak/null control? Then go with the two 500s with one centered up front and one centered on the rear wall (or both side walls, but the others are acoustically better according to some).

Do you want to tame the bass/LFE madness found in all rooms and can sacrifice the space, then go with four EP400s with one centered on each of the four walls.

Farewell - June 4, 2020