Enthusiastic critique always is welcome! (Although I find enthusiastic in-the-room critique of vastly greater probative value than remote video critique.)
I am hearing largely the same thing as you and as Peter in direction, but not in amplitude, so to speak.
In other words I hear clearly in the room the bass bump around 60Hz. It's an audible boom which masks texture and detail somewhat above and somewhat below that frequency. (In fact the reason I started with the real time analyzer measurements is because I subjectively heard early on the 60Hz room boom myself.) This is definitely a mechanical problem to be solved with a mechanical solution.
Subjectively, the bass frequencies should not be drawing attention to themselves, but I am not personally looking for a subjectively perceived flat bass response.
The ribbon drivers put out a lot of energy, more energy than the Magnepan 1.6s. Some visitors are perceiving this as a little bit bright in the upper midrange, other visitors are not. I am perceiving it as a little bit bright in the upper midrange, especially on LP. I hear it as a touch shrill on certain piano key licks.
Ideally, for my ears, I will be able to dampen some of this upper midrange energy. I would like to nudge lower the perceived sonic center of gravity of the system. This is where loudspeaker toe-in experimentation (although such experimentation so far has suggested that the sound doesn't change very much) and some acoustic treatment experimentation, and maybe some amplifier tube swapping, will come in.
No loudspeaker is perfect, in my opinion. These speakers are never going to have the upper bass/lower midrange sonic center of gravity we hear and like from David's Bionors. There are specific reasons I prefer panels in general and these speakers in particular to Bionors and to other vintage loudspeakers which have a similar (and very natural to my ears) upper bass/lower midrange sonic center of gravity. And yet as natural as those loudspeakers sound, I sometimes can't avoid the nagging sense that "something is missing."
In summary, the bass emphasis is an objective problem needing fixing. Specifically, I would like to shave off that 5dB bump circled in red. The upper midrange energy is more subjective and more complicated. I and others hear it more on LP than on tape. Ideally, I will be able to tamp it down a little bit.
