Eagle, besides the martin logan look at the Velodyne MiniVee or SPL8 subs. They have a small foot print but big sound. All three of these have very tight, clean sounding bass and are great for music and good for HT. Also consider some of the lower priced T series REL subs. www.sumikoaudio.net REL makes some of the best subs in the world!

You can find that ML sub at best buy magnolia, its very musical with no boom or muddiness. It has a small foot print as well.