I have the EV ZLX12-P's They are far from flat. Scooped sounding. I use them for vocal monitors or sometimes FOH. My FRFR is a JBL prx612m. Sounds like your problem is the room(s) more than the FRFR. Esp if you get a good sound at gig volume before the rehearsal. Rooms esp smaller ones with low ceilings and hard surfaces have all sorts of problems. There is software to figure this out. My old rehearsal space had a natural bump at 300-500hz and all sorts of reflections. I always wondered why my Marshall sounded fine at rehearsal and thin at some venues. One set patch will not sound the same in different rooms no matter what FRFR you have. So I'd just build a few patches for live with the horn band where they play and be done with it. Or go IEM and that's a whole nother can of worms...