["analogj I'm aware of what subs CAN do, but I have never heard a sub, even in an audio salon, where I didn't ultimately prefer the sound of the main speakers without them, at least for music."]
If you heard the sub, even in an audio salon, I believe it wasn't, or simply incapable of being properly set up.
In my experience the upper frequencies benefit from more space not the bass. The earlier 18" version of my current Room Optimization equipped 10" subwoofer used in my 10'x10'x8' studio are only distinguishable when turned off during play.
All the best with your search.