Considering a POSSIBLE replacement for speakers. Opinions?

Maybe try the Audiophiles guide by PS Audio? Perhaps you have exactly what is needed, minus proper setup?

Spatial M5 Sapphire or the M3’s for $5k. Check out New Record Day’s YouTube review on the M3’s

I would do yourself a favor and try to listen to a good american vintage speaker made before 1979 they will shock you in so many ways on all types of music and you will have an heirloom to pass down to the rest of your family.

I recently undertook the same search with the same upper limit. I currently have Monitor Audio speakers (Bronze 5 I think) and considered, in no particular order:
Monitor Audio (I forget which ones)
Klipsch (but a newer version of the one I considered came out and was priced above the $4k limit)
Sierra Tower
LSA-20 (the more expensive one, most likely, as they are regularly on sale for $3k without a trial or a bit more with one)
Spatial M5 (would have preferred the M3, but they were above my limit)
Raven CeLest'
Decware speakers (considered a few)
Ohm Walsh
Salk speakers

I discarded the Klipsch after reading a couple reviews; other reviews suggested that the Salk speakers that were best for rock were above my price range), and I knocked out others that needed to be too far from the wall or too close to a corner. I was leaning toward the Sierra Tower or the LSA-20 had I gone for a more conventional speaker or the Spatial M5 if I thought they would work in my room (it's in a weird position). I decided on Decware ERR-x given my room dimensions. Will know in a couple months if I made a good choice.

Good luck deciding!

I have Monitor Audio Platinum PL300 II and couldn't be happier. I have always loved the musical side of M.A., coming from being a Klipsch Heritage line owner for many years. The M.A Silver line has always been a favorite, very nice sound, good luck on the hunt.