Very good points.
By 'coherence' I mean that all frequencies have the same character, which is hard to get when treble comes from a beryllium tweeter and bass comes from a paper cone, but easy to get when they all come from the same membrane. To get that in the HT I went to 6 MMW's, 2 DWM's, and 1 Quad 2905 (centre), with Bryston amps. These Magnepans are all based on the older planar-magnetic technology rather than the quasi-ribbons or ribbons, which may have been a mistake - but I knew that I loved that sound, and in the HT it's a wonderful, engaging, immersive, coherent sound.
Magnepan DWM goes down to a usable 37Hz in my room, so the big 20.7 or 30.7 should do that too - recall that they use the same bass technology as the DWM. I haven't heard the 20.7 or 30.7, so check that the ribbons integrate well with the planar-magnetic panels.
And of course, your room is its own study, so YMMV with the bass response. It's an ongoing journey, but you're starting at a very good place.