There's no reason to think that more capable subs can't be as musical.
Will this system be primarily for music or movies?
You have a physics problem; that room has a lot of air to move around. Whether for movies or music, for the sub to be "effective", you're going to have to drive it pretty hard. I'm just not sure that something like an EP175 is going to be able to move enough air cleanly to give you the results you'd like.
Consulting the fine folks at Axiom is always a good idea.
My room is much bigger than yours (relative to cubic feet); I have a relatively modest SVS PB12-ISD and feel more than adequately served. Since you already own an SVS, you are probably used to similar performance.
