Rythmik Audio with their sealed design and servo technology are hard to beat for their price point. Fast, articulate, musical with absolutely no flab or boominess. I chose them for the very reason you are looking for a sub... music first HT, second. Due to the size of my room I bought two F-15's from Rythmik Audio. That's a ton of bass for the money. Highly recommend them.
FYI, Rythmik drivers are quite popular in the DIY market.
FYI, Rythmik drivers are quite popular in the DIY market.