Morricab, that is a wonderfully written OP. You really describe well the sound and experience of listening to those two cellists up close in an intimate setting. It would be great to see a photo, if you happened to take one. I like the descriptions of how visceral it was, and the tonal density and sense of presence. The sound and music, filling the room. This is what live music in such a setting is all about. I marvel at the sheer vibrational energy resonating out of a cello. I, too, have never heard a system do that. However, I have heard a very small number of systems come pretty close to reproducing the tone, presence and energy of a cello, at least enough to be convincing and believable. Two were cones driven by SS. One particularly poor system was a pair of Altec horns driven by SETs. We all have different examples.
I was excited to read your opening post and had hoped this thread would encourage a discussion about "Live music, Tone and Presence." What are they and why are so many systems disappointing? We hear these things when listening to live acoustic music and we have heard some systems succeed and many fail at portraying these characteristics. There have been many posts in this fascinating thread in just one day, but sadly, they are mostly about the old topic of SS versus tube, or SET versus push-pull, or horns versus cones. Is this how you would like your thread to develop? I don't have a lot of experience listening to many different systems or component typologies, but I can say that I have heard tube, SS, cone and horn based systems convincingly portray "tone, presence, and dynamics", to quote Jim Smith's triumvirate.
I agree that many systems get these wrong, but I no longer think it is about typology. I think it is more about the quality of the design, and how the system and room are assembled and set up. I have learned to be increasingly open minded about what kind of components or system can produce a convincingly musical experience. Hearing those cellos as you did, gives you a good basis on which to judge a system's success. Thank you for sharing that listening experience with us.