Most impactful for playing soft

I have also observed the better the system, the better it sounds at low volume. Each tier up sounded better at lower volumes. I suspect that there is more to it than that. That a sub $100K system can sound great at really low volume. But I am unsure as to what it would be. But once my system broke $100K it started sounding spectacular at low volume.

Yes, best of luck. This sounds like a decade or longer search to find the key.

A receiver with a loudness control :)

@secretguy -  

         A receiver with a loudness control :)

                                 OR: DSP

      (with which to program a little boost, at times*)

  But: let's not deprive the fact resistant of their beloved chasing-of-the-tail (with *the answer).

https://www.extron.com/article/loudnesscontrol_ts#:~:text=The%20loudness%20control%20is%20simply,treble%20appear%20to%20be%20lacking.

@milog -

     One can preprogram a number of freq response ("loudness") curves, with one of these devices, for those special times:

       https://www.minidsp.com/applications/dsp-basics/system-equalization