Well, this is a solid starting point to try to determine the maximum possible dynamic range in a typical room for high fidelity music reproduction.
We can use just 2 diagrams, the first is the average room noise and the second is the 100 phon curve, the maximum tolerable sound level, the pain levels.
View attachment 51781
View attachment 51782
At 20 Hz, listening threshold is at 65 dB's and lets assume that you have the best possible subs to get 130dB's over there to match the 100 phon curve, so the maximum (perceivable by our ears) possible dynamic range is 65 dB's.
At 80 Hz, the average room noise is at 35 dB's and lets assume that you have good speakers to get 105dB's, so maximum possible dynamic range is 70 dB's.
At 1 kHz, the average room noise is at 10 dB's and pain starts at 100dB's over there, so maximum possible dynamic range is 90 dB's at a really really quite room, and i think that 20 dB's of room noise is quite common, so you have 80 dB's of maximum possible dynamic range.
At 10 kHz, listening threshold is at 15 dB's (for very young people) and pain starts at 115dB's over there, so maximum possible dynamic range for a child is 100 dB's, but a child cannot bare so high levels (that's why they are "estimated") and an adult can hear nothing at 15 dB's, so you can say with confidence that the maximum possible dynamic range is between 80-90 dB's over there, depending from age.
Keep in mind, that if you are listening to high levels, the ear has a mechanism of lowering it's sensitivity to adjust at these high levels, and the threshold is raised for a short period, which means that although you may hear a tone at 20 dB's in mid frequencies when your ears are adjusted in a quiet room for enough time, if you listen to music at 100 dB's for more than a minute, then for a 2-5 minutes period you hear absolutely nothing at 20 dB's.
I assume that you can all agree that the maximum possible dynamic range for human hearing, in a quiet room, is frequency depended and it is in the range of 65-80 dB's, and maybe, a little more, just in theory...
I suppose that a dynamic range of 70 dB is a perfect goal for a sound system, and also quite difficult to reach, because your speakers must be able to reach almost 125 dB's at 20 Hz... (The 90 phon curve).
In a real life example, you stated that you were surprised how quickly the enormous lp surface noise disappeared when the music started, at your test of musical fidelity phono stage. The dynamic range of that recording, could not be more that 35 dB's, the sinad and dynamic range of the phono stage is there to see, and i suppose that you were not listening at 125 dB's...
Anyway, i think that you may have to change the maximum possible dynamic range for human hearing at music reproduction, at about 70-80 dB's, and anyway, even in theory, never over 90 dB's.
115? I really don't think so.