I suspect it’s the room. Throwing money at cables, other speakers, and so forth, seems ill-advised. And don’t some audiophiles just LOVE to spend lots of money in in their pursuit of Nirvana?
Perhaps contacting one of the acoustic panel companies for a consultation would prove to be beneficial. One of the most effective and economical improvements is SQ I’ve made was to assemble 2’ x 4’ x 6" bass traps for the front corners on my rather "bright-sounding" listening room. The 6 Owens-Corning sheets cost about $100, wood for frames about $35, and some inexpensive white burlap about $40. I plan to make a few more thinner (2") panels for first reflection points, and perhaps elsewhere.