Raising surrounds higher, especially the rear surrounds, is also my suggestion, but given they are in custom wall cavities (which btw hurt the sound), least I'd do is to flip them 180 degrees to put the tweeter on top, stead of the bottom.
Left/Center/Right are in most dire need to be upgraded. Tons of good options - depends on your budget.
An acoustically transparent screen would also be my choice in the dedicated HT room and I'd go with ugliest and best-performing speakers I could find and place them behind the screen. JTR, PSA or maybe DIYSoundgroup one of the Fusions:
https://www.diysoundgroup.com/home-...home-theater-series/home-theater-fusions.html