@richopp, I bought my first Maggies---the Tympani T-I---in ’73, and loved what they did well. But I missed the liquid-transparency and "snap" of ESL’s (the early Maggies were a tad veiled and soft), and the bottom octave (we didn’t at that time know about bracing the panels). So when in ’74 the Fulton Model J was introduced, I sold the Tympanis and bought a pair.
It didn’t take long for me to regret that move: yes, the Fulton was more transparent (those RTR ESL tweeters were about the best available at the time), and had "shuddery"/deep, deep bass, but lacked the wide-open sound (the sound box speakers produce seems to be squeezed through the boxes) and lifesize images (big instruments sound like dollhouse miniatures through small loudspeakers) of planars. I experienced planar-withdrawal! I sold the Fultons and have been a panel-lover ever since (current owner of Tympani T-IVa, Eminent Technology LFT-8b, and original Quad ESL)..
But to get deep bass out of planars, the panels have to be very large (Tympani double bass panels---or the new 30.7, and SoundLab ESL’s). That Tympani bass is unlike that produced by any dynamic woofer I’ve ever heard, until I heard a really good OB/Dipole (there have been some poor ones, like those Gradient made for Quads). For those not having room for the 36" wide (each channel!) Tympani bass panels, these prototype 12" wide Magnepan OB subs are a very welcome alternative.
Sure, the GR Research/Rythmik OB/Dipole Sub has been available for almost ten years (and is fantastic!), but it is available only as a DIY kit, the H- or W-frames the kit (in basic form a pair of 12" servo-feedback woofers and associated plate amp) is installed in needing to be built (there are easy-to-assemble flat packs available). Many audiophiles have no interest in anything DIY, so again, the possibility of a commercially-available OB/Dipole sub, especially one designed specifically for Magneplanar loudspeakers, is of great interest. While no substitute for big panels, an OB/Dipole sub is as close as you can get to the taut, percussive (piano! drums! slapped upright bass! Yo Yo Ma's attack on his cello!) bass impact that planars produce.