If you want to stick with Axiom, and watch mostly TV/movies, I would consider the EP500 (I own one). It won't disappoint when it comes to HT AND music. The EP400, from what I've read and heard, is more for smaller rooms for music (as jakewash said). However, at the EP500's price point, there is no reason not to consider offerings from other companies, especially if value is a high concern. Especially also, IMO, if you mostly watch TV/movies.
I have not heard the EP600, but again from what I've read on this forum from others that have compared them, the differences between the EP500 and EP600 are subtle. The EP600 is said to perform better with music and go a little lower.
