I am looking to upgrade my current Def Tech 15TL with a nicer sub. My room is a 21X15, I like the sound of the 15" drivers. My main speakers are B&W CDM-9NT. Use is about 50/50 movie/music (including SACD/DVD-A). So far I am leaning between the HGS 15II or X or the SVS (although only 12" there). I need to have a box shape and the size matters, I need to have a fairly small box (as possible). Any recommendations would be greatly appreciated. Thanks!