I've coupled a bunch of subs with a pair of M3Tis driven by a 5 watt per channel single end triode ASL MG S1 15DT in a 2 channel stereo system.
I've used both the Velodyne CHT80 and CHT100 (8" and 10") these are very nice subs, very tight and musical.
The Vance Dickason Titanic 10" from partsexpress.com is a bargain, easy to assemble kit delivered for $350. Very strong bass, very musical.
I found a Dahlquist PDQ1500 15" sub for about $100 on ubid a while ago when that auction site was active and full of bargains. It is a wonderful sub, especially if you take it apart and stick some acoustic foam to the cabinet and give it a bit of stuffing. This model is out of production, but if you can find one at a good price, I recommend you GRAB IT.
I don't like the sunfire subs. To my ears they sound like one note thumpers. The Klipsch LF10 (rated at 1640 watts) on the other hand is a small cube with an active 10" and a pair of passive 10" radiators. Sounds excellent. Very strong, very musical.
I have an old Kenwood SW300 10" sub whose driver I blew to pieces playing the Time Machine (Dream Works version) I replaced the Kenwood driver with a 10" Titanic driver from partsexpress.com. What a difference! This sub now rates with the best of the ones described above.
I picked up a gigantic SVS 20-39, but didn't use it with the M3s. It is extremely musical, and an extremely powerful bass generator for movies. Probably would be an interesting combo, small bookshelf speakers coupled with an industrial water heater sized sub. By far the best sub of the bunch I've tried.
