but the thing that stand out in my memory when I have heard live music is often the dynamics. It’s those dynamics and how an artist plays with them that often causes the hair to stand up on my arms. But I’ve never heard a stereo system accurately reproduce these dynamics in a home system or demo at a show. Not even close. It’s always constrained.
You're making blanket statements about live music that don't often match my experience. I hear live music a lot, in several venues, and I have recorded live instruments for the purpose of assessing my system, and sometimes the dynamics are greater because the music is louder, but often not. Often symphony performances do not get very loud, especially if you're sitting about midway back in a decently sized auditorium. The loudest I measured at our seats for a orchestra playing Beethoven's 9th symphony a couple of years back was only about 93db on a crescendo. Averages are more in the 70-80db range. Live acoustic jazz in a restaurant that seats a hundred people is not going to be all that loud either. I've never measured a performance approaching 95db. Chamber music in a ballroom venue... maybe you get peaks of 90db, seldom more, unless you're very close to musicians.
All bets are off with amplified music. My wife played in an amplified rock covers band some years ago where I measuring about 100db average at 20 feet. That's not a typo. Her drums were the only unamplified instrument. I stopping going to the gigs and made her wear earplugs. Electric guitars, keyboards, basses, and horns with a mike in the bell can be arbitrarily loud, but this stuff isn't reality. You're listening to an electronic, contrived performance; it can be anything the musicians want it to be.
She also plays in a local big band that performs in public venues. They can get quite loud because the venues are usually too small for such a large group or inappropriate, like having a lot of glass. No one would want a recording of those performances, even though IMO the musicians are quite good. Could a descent system reproduce that? I doubt it; the venue defines the sound, but not in a good way.
Instruments are louder in small rooms, like 99% of residential venues. Multiple people have been surprised by how loud her 4.3 octave marimba can be in her studio. I've already mentioned her biggest drum kit. But in commercial venues unamplified instruments aren't typically approaching 100db. A marimba is suddenly not all that impressive. Perhaps a saxophone or a show-off drum kit gets really loud, but even our upright Steinway in her studio is realistically reproducible. A violin in a small room (e.g. 3000 cubic feet) can be loud, but how many recordings are made this way? Woodwinds... easily reproducible. My step daughter is flautist, she has a BA degree in music from a top university, and I once had her play along with a studio recording of herself for a university audition while standing between my old Legacy Focus speakers, and the realism of the effect was mesmerizing, but not magic.
I read about the unapproachability of live dynamics in Stereophile and other audiophile sites and publications, and have for years, but this doesn't align with most of my experiences except in rare situations. Like a live jazz band with multiple horns in a small to medium size venue playing very loudly. I wear earplugs for those events. Live music can be very engaging and better than you can hear in a residential room, but it isn't the voice of God either.
All of that said, music sounds different if it isn't reproduced at the same volume it was recorded. I think a lot of systems have more distortion reproducing 92db at a listening seat than most people want to admit. I suspect distortion is the reason most people can't listen to their audio systems for as long without fatigue as they can listen to live music at similar volumes.
One other comment. I think there are two kinds of audio enthusiasts around. I'll call them "sounds good" and "sounds accurate". Almost every enthusiast I've ever met is in the "sounds good" camp, and I was until about 2003, and then I started hearing more live music, and recording instruments to assess my system. What a mistake! Caring about accuracy is the worst thing that ever happened to me, audio system-wise. It was easier to enjoy my systems when all I cared about was if they sounded good. IMO, you can always tell a "sounds good" person just by their subs - they're always run too hot. They have favorite music that shows off their systems. They watch action movies they know are dumb just to hear their equipment. Unfortunately, I can't go back. My brain is ruined forever.