I use the same electronics as Bob's friend (Velodyne SMS and NHT x-2) with Rythmik subs. This combo works well with Maggies - not Quads, but cut from similar cloth (if you'll pardon the pun). I suspect that there are many fine subwoofers out there that will work well, but I attribute most of the credit for my successful set-up to the aforementioned electronics.
Good Luck
Marty
Good Luck
Marty