I doubt you will improve that with Eq, and may well make it a lot worse.
There are just too many rules broken.
It is an above fireplace installation which is very bad. The system to too high, and all the speakers are against a hard stone wall. In addition the speakers are all far too close together, causing massive comb filtering issues.
One thing you could try is to move the right and left speakers 7 to 8 ft or more apart.
If you can't do that, then I would get rid of the center speaker. I think it would sound a lot better without it given the current layout.
I can't let you down more gently, but that is a system that should NEVER have seen the light of day. That is a pity as it is pretty good gear.
I'm in the middle of a new house build as we just sold out lake home.
My wife wants "her system" as discreet as possible in the min level great room. This will be a secondary system. These type of systems are not as easy as they look.
This is the system so far.
Note that the system is not above the fireplace, but to one side of it.
The tweeters are optimal at 36" above the floor, and the tweeters of the right and left speakers just over 7' apart. I have designed the speakers as in walls from the ground up. Even so, I fully anticipate that the computer modelling will not be perfect and that the speakers will need additional voicing after completion based on measurements and listening.
The bottom line is that these type of system look simple and straightforward, but in reality they are anything but.