Troy,
Have the same speaker set-up and you. Originally I had a Definitive Technology sub but now I just purchased an EP600 and I'm thrilled with it. My room is about the same size as yours so I know it does the job. Price is always a factor and seeing the quality of Axiom products I'm very sure you'd be happy with any of their subs. Don't be fooled, matching same products within the line is always a plus. In terms of room I if you can fit any of the smaller subs you can also fit the EP600. It's footprint is about the same and it carries it's expanse in height rather than floorspace. I've heard other makes and models and they differ mostly in power but most seem to provide the same kind of bass. I was extremely surprised at how different the Axiom sub was from others I've owned and or heard. They truely are in a class by themselves. I think it's worth the effort for you, if you can, to arrage a demo hopefully with a near by owner.
Good luck.

www.thedigitalcinema.net