Yep Marty, the ET’s woofer is it’s weakness all right (as is the woofer in any and all planar/cone woofer hybrids---with one exception. Read on!). I don’t use it, just leaving the woofer jumpers on the x/o unconnected, running only the panels down to the factory x/o frequency of 180Hz. I use the GR Research OB/Dipole sub in it’s place. The OB sub can x/o as high as 300Hz (though I cross it over at 180, same as the stock ET), and puts out bass with the same sound quality and character as the panels (no, really!) but goes lower and plays louder. True pure dipole sound from 20Hz to 20kHz!
The sub can be added to any planar, and I would even if I had 3.7i’s (or even 20.7’s). It even blends seamlessly with ultra-transparent ESL’s (I used it first with my Quad 57’s). I’m gonna sell one of vintage drum kits to finance another pair, stacking the OB H-frames two high. They’ll be 5’ tall, exactly the same as the ET panels. Four 12" Servo-Feedback OB/Dipole woofers and the ET magnetic-planar panels (whose main driver covers 180Hz-10kHz, with no x/o and in true push/pull balanced operation, unlike the single-ended Maggies) per side.....like the Infinity RS-1b (which I owned for a few years, Brooks Berdan’s personal pair), only much better!