It was Roger’s electrostatic loudspeaker that I thought was the last product he introduced as a "stock" (at least by Modjeski standards ;-) Music Reference model. And I understood it to be available either with or without the direct-drive OTL amps. Perhaps that too is a myth.
I DO know his ESL included dynamic woofers (for 100Hz down). Roger told me he considered the bass of the Quad ESL to be inadequate, that the bass panels had a resonance which could not be eliminated. As I said, he advised me to use a symmetrical 24dB/octave filter when employing a sub (I’m inclined to consider a driver coming in at 100 Hz for use with a planar as a woofer, not a sub, but that’’s just a matter of semantics I suppose) with the Quad, necessary to make the resonance inaudible. As his own ESL included a "sub", and as he told me he considered the Quad’s bass reproduction to be inadequate, and was adamant that the x/o filter be steep, I guess I just came away with the assumption that he used a dynamic woofer with his Quads. I am in fact surprised he didn’t. For Quad owners looking for a woofer, the Rythmik plate amps include a 24dB/octave settings on their crossovers.
Roger stated in his Music Reference AudioCircle postings that of the MR amps returned to him for repair, it was most often as a consequence of botched modifications, usually for nothing more than the replacement of his stock parts with "magic" parts of the same value (including "magic" fuses ;-). When looking for MR amps I therefore always made sure the ones I bought were unmolested, 100% stock. I got my RM-9 from Sheila Berdan, and as Brooks was a MR dealer the amp may have originally been bought from him. Kismet? ;-)
As to the "lightweight" sound of the RM-10: when mated with a typical high-sensitivity loudspeaker, that may actually make for a synergistic pairing. Many of them have bass I would characterize as "woolly" (not a fan of the bass-reflex design).