All right beernut, I wasn't going to go here, but georgelofi's post above changed my mind. I earlier recommended the Rythmik subs, which feature designer/owner Brian Ding's patented Direct Servo Feedback circuit and a number of different woofer and amp choices. Any Rythmik sub will sound great with your Maggies, but there is one even better choice.
Brian collaborated with Danny Richie of GR Research in designing a woofer optimized specifically for OB (Open Baffle) use (along with a "shelving" circuit to compensate for the low-frequency roll-off inherent in dipole design), and this woofer too is controlled by the servo feedback circuit in the Rythmik plate amp. The woofer is available in 8" and 12" sizes, and its OB-optimized design, combined with the Servo Feedback control, results in a very "fast" sounding sub. With either driver, a sub particularly suited to use with any and all planar loudspeakers can be had---the GR Research/Rythmik OB/Dipole Sub. The woofers (either two or three per sub) are installed in an open baffle frame, resulting in a sub sharing the planar speakers figure-of-8 polar radiation characteristic. You can read about it on the GR Research website, and the GR Audiocircle Forum. Don't buy a sub until you have considered this very special one!
