A sub is a good thing for movies, no matter how good the mains are. Floor standers are designed for music, where very seldomly you find anything below 40 Hz. Musical instruments just don't go that low, maybe organs...
For a smal to medium room, I fully hartedly recommend Sunfire Dominator 8, currently on sale for $450 at audioadvisor.com. Thay are extremely musical as well, their bass is tight and accurate and are very small. Thay are a superb value. They rattle the house with moovies and complement the mains for music very accurately.