I listened to a Bag End INFRA 12" Professional today, and while I know there is some contriversy regarding Bag End's approach to subwoofers... I'm a massive fan of their monitors (probably the best sounding speakers I've ever owned, regardless of how hesitant I was to listen to them), and the 12" I listened to today was by far not the loudest 12" I have heard, but it wouldn't bottom out because it protects itself with increasing the lowcut dynamically as needed to prevent any distrotion...complete with a red light letting you know). But when I wasn't abusing it, I heard the cleanest sounding, aligned, realistic, powerful, pined at the core bass I have ever heard. It handled the lows so well, it made my other subwoofers look embarrassing, sloppy.
http://mixonline.com/mag/audio_bag_end_infrasub/
http://mixonline.com/news/audio_aes_bag_end/
http://remixmag.com/mag/remix_bag_end_infrasub/
Home theater there are certainly better choices, because time-alignment doesn't matter too much when the robot is crushing the squirell or something. But, I'll tell ya, for mixing, I think I'm gunna order one of these on Monday.... like... I /have/ to have it to go with my PM6s.