An EP500 in your room size is serious overkill, which isn't bad, just excessive, which can be fun :D.

I have an SVS sub that powerwise is close to the EP500 in my room (again, about 1750 ft^3) and it's riciculous... WAY louder than you would ever actually ever want it to be.

The 500 would reach a few db's lower though for movies obviously. I wouldn't consider the 400 for you, I am pretty certain it is much more of a musical sub.