No disrespect, but I think your statements have inaccuracies.
The average SPL that a musician works with is 100dB. A singer will usually surpass that volume if they are really belting it out. Relatively speaking to a non-musician, that is quite loud, but to a musician, this isn’t loud at all.
When the hearing instrument on the input side is in distortion, all other signal going to the output stage is going to also be distorted. However it has nothing to do with the output when we are talking about high SPL inputs.
So, when you have a hearing aid that is set up to receive that level of sound, then the output should also be nice and clear with no distortion on the highs or lows.
I’m glad to know you know of the Unitron musician hearing aids. Not many people do.
Cheers!