Multipel Driver Subs

Other than Vandersteen and Martin Logan, are there any other good multi-driver subwoofer designs? Essentially, I'm looking for something considered to have a 'quick' response to match to Magnepans.

The biggest problem mating mono-pole subs with di-pole speakers, is the way that each interacts with the room.

Any "good" sub will mate well with Magnepan speakers as long as you cross over at 80hz or below.......I use 65 hz with my Apogee speakers.

"Quick" has nothing to do with it..........the Maggies are no quicker than any other good speaker on the market (if they are, they are playing the wrong freq's)

Your best bet would be to use di-pole subwoofers with the maggies?

Rel's, Velodyne and especially Definitive Technology (one active and 2 passive drivers) match well with Maggies.
The JL Audio Fathom F212 was the best match for my Dali Megaline. The Megaline uses a seven foot dipole ribbon (per channel) that operates from about 1000 HZ on out, similar goals of dispersion and speed as the Maggie dipole ribbon design.

The JL subs are a superb match for my twenty four 6.5" woofers which are quick and rear ported. The subs are absolutely invisible musically, except I have very low bass previously missing.

I run them as a stereo pair in my system, I bet the JL would be a super match for your Maggies too. They should cross low as Dave and I have both suggested.
IME (reasonably extensive) sub-matching is a two step process, neither of which involve the "speed" of small drivers. The first step is matching the sub to the room - optimized with proper output capability, careful placement, multiple subs and /or parametric EQ. The second step is matching to the speaker. This involves finding the right crossover point and VERY careful level matching.

IMHO, the "speed" issue is more a function of the sub's damping than driver size and can best be represented by the "group delay" spec. Usually (but not always) sealed subs exhibit the lowest group delay and provide the fast (or maybe more acurately, "tight") bass that mates best with certain speakers.

SVS, and Rythmik (my choice) among others offer variable damping with makes matching easier. I also use a parametric EQ unit (Velodyne SMS-1) to smooth response and optimize the "handoff" from speaker to sub. The Maggies I use (SMG) presented some challenges, but - in the end -I got the precise result I was seeking.

Good Luck