Great topic, but I find it almost more intriguing that your 7-year-old would request Einstein on the Beach. I bought the Tomato 3-album set in NYC back in the 70s, after I walked into a record store and heard the end of side 1 playing, where everything just goes nuts. Later I sold the set to a friend, but last year I found the same set for a few bucks at the used record store, so I grabbed it. After I got home, I realized there were 2 copies of disc 2, and no disc 3, but I suspect the original owners had never noticed.
One day I was cranking up side 1, when my family staged a revolt and demanded I take it off -- and they were all outside working in the yard! I will say though that on a long car trip when my kids were quite a bit younger, I played all of A Love Supreme. About halfway through I asked them if they wanted me to take it off, and they both said no, leave it on, and they continued listening quietly to the whole CD.
As to the original question, I too try to approximate true performance levels, at least with classical and jazz. One thing I don't like is turning up a quartet, say, louder than it would be in person. But violins are surprisingly loud.
I recently measured the SPL at my typical listening level -- I normally set the volume about 11 o'clock, which seems pretty loud to me. I was kind of surprised to see it was only about 80-85dB. I was happy too, because you can listen to that all day and not damage your ears. One o'clock is the highest I ever go, and that is about 90dB.
I play music professionally (acoustic and electric guitar), and I know the drums are well above 90dB. But I wear earplugs then, which is not something I would want to do listening to my stereo. In other words, even when I listen to rock I crank it up, but not to truly realistic levels.