The specs on the svs pb13u looks phenomenal, although it costs more than the ep500. It also has a lot more adjustments than the ep500 has. I'm going to have to study this one a little more. I don't like the idea of losing Axiom's customer service on a product, though, so for me the ep500 may be worth it just for that.
Edit: Price wise though, I would probably rather have the ep600 for about $100 more than the pb13u. So, I think I'll just stick with the EP500.
As a PB13 Ultra owner I can highly recommend it. It works great for movies - reaches real low and is smooth enough for music to almost equal Axiom's offerings for music playback.