As I’m sitting here reading all this, my mind wondered to room treatments. Have you measured out the first reflection points on your front wall and ceiling? I to have a doorway next to a speaker and it noticeably messes up the sound, but I covered up my fireplace and put a 2’x4’ absorbing panel above it and for the other side, I bought one of those cheap folding walls and tossed a comforter over it. I have to take it down when company comes, but that’s easy enough. The only thing I haven’t been given permission for, is to put panels on the ceiling, but I’m thinking you might have to really consider it. Oh, and those smaller corner bass traps, do help a bit. ( but once again, they were not wife approved here.)
All the best.