WC,
I understand and agree with your 4 pros and 4 cons about the 20.7 with Mephisto. Your present 20.7 system with all the top supporting components is possibly the finest 20.7 system in existence. Few Maggie owners have the quality of supporting components you do, largely because of bad industry-wide marketing that advises people to use cheap and expensive components with cheap and expensive speakers, respectively. However, the company says that some customers do have more expensive components. Magnepan should pay you to accommodate listeners who really want to hear what Maggies can do.
Your Alexia 2 system is possibly the finest such system, since top components are also used, but the Mephisto enables true appreciation of the differences between the two speakers. I went back and forth between the latest video with the 20.7 and the last video with the Wilson, using the same music. I think the 20.7 was recorded a little louder than the Wilson, so I adjusted the volumes as I compared.
Using my mediocre stock iMac audio, I cannot judge bass, imaging and spatiality, but I can compare the tonal qualities of each system. Yes, the 20.7 has a fine tweeter, but so does the Wilson. What makes the 20.7 my choice is the rest of the range, due to the low mass planar drivers, and the open baffle, boxless design. You can hear how the 20.7 presents voices and instruments most naturally as they are in real life, without the overlay of artificial resonances that come from boxes. The 20.7 shows the beautiful woman with a thin layer of clothing, but the Wilson shows her in a thicker coat so her fine features are obliterated to an extent. Obviously, she appears fuller in the thicker coat. So the fullness comes at the expense of natural detail. You can hear the true tonal character and detail of voices and instruments with the 20.7. Spatiality benefits also as the whole freq range of timbres is fully revealed.
This got me to thinking about the many dynamic speakers available using the open baffle (OB) design. Tweak1 writes that he had the Maggie 3.5 but couldn't get the ribbon tweeter to integrate with the rest of the range, to his satisfaction. So he got various Emerald Physics OB models, and got the natural detailed sound of his 3.5 plus more dynamics from the dynamic drivers used. I searched "open baffle speaker" on Agon. On the 1st page, look for the entries, "Spatial Audio M3 Turbo S open baffle speaker review" and "My new review of the Spatial Hologram M4 open baffle speaker." Since I have trouble linking whole articles, I excerpted from the Hologram review some pertinent statements that echo what I have been saying about the supreme importance of tonal quality.
"I now understand what posters on speaker forums mean when they say things like, 'Tone is everything. What good are imaging and bass extension if the instruments don’t sound like what they are?'
"This is one way in which the Hologram M4’s truly excel. They are masters of tone. Trumpets, saxophones and other wind instruments sound very real. Orchestral strings sound sweet and woody, with the shimmer of the real thing. Voices are as palpable, expressive and human as the best single driver designs that I’ve heard, and that’s really saying something."
Read his whole article, which I think is spot-on. He says much of the high cost of excellent speakers with box designs is that of the materials and engineering to make the box sound as boxless as possible, while attempting to get the powerful dynamics that come from box reinforcement. Personally, I believe that no box speaker can compete with a boxless design for absolutely natural lifelike sound The top Wilson Chronosonics are probably the best Wilsons, mainly because they best implement time alignment through their concave driver configuration, but before anyone spends $600K on Chronosonics they should listen to top OB speakers. Spatial sells direct for as low as $2K or less, and their top Lumin line starts at $20K. The Hologram M4 was $1300 at the time of the 2016 post. Clayton Shaw designed the Emerald Physics line before moving on to Spatial.
So my latest thinking is that for ultimate natural sound, OB offers the best prospects. Then the question comes down to which driver technology offers the closest simulation of natural voices and instruments. I still believe that lowest mass drivers like planar magnetics, ribbons, and electrostatics offer this. But OB dynamic drivers can now compete with those low mass drivers, and offer more dynamics to boot. The low mass drivers offer maximum purity with less bass. Take your choice.
So the 20.7 and ML 13A comparison will be most interesting.