IME, the issue w/MMGs and subs is optimizing the integration of the subs and the panels. It's tricky and IMHO depends on the getting x-over done properly as much as choosing the particular sub.
If you have an Audyssey (or equivalent) equipped pre-pro, you're golden, and you have a wide array of subwoofer choices that would, I suspect, work pretty well. If you do not, you might look at the Velodyne DD subs, which include their own integration software. It's a PITA (because the auto set-up sucks and it consequently requires endless manual tweaking for best results), but...if you're willing to spend the time to get it right... it works well.
Good Luck
Marty
