The HSU, the PE, and the SVS are all outstanding subs. Decide if you want it for music first, then movies, or vice versa. SVS for movies, HSU for music, and PE for high output and a mix of movies and music.
PE makes a nice sealed 15" entry level unit for under $300. It's model 300-770 and may be a perfect fit your your system. I don't think you can beat it for the price.