How to tame brightness

Try different toe in, more,less, loudspeaker may have a on axis peak in response this could reduce it. Also address room acoustics if you have not, might but be a reflection off side wall floor etc.

I agree with attacking the acoustics first since this is where a smart 'file begins the quest to get great (best) sound. If you can take the brightest sounding system/room and turn it into a dull mush by overdoing sound treatment, then your happy medium obviously lies somewhere in between. If you have slap echo, you're gong to have bright sound. Start with the 1st reflections then the room tri-corners where slap echo lives.

While I agree that felt is a good thing because diffraction sucks, diffractions usually affect imaging more than anything else.

the Epos tend to get sharp/edgy/hazy/shrill

This is a characteristic with Epos. Been through this with B&W. While I tried all reasonable solutions (including covering all the walls with blankets), in the end I found no good solution in adding one error to compensate for another. It was a bitter pill but had to dissolve the entire system.

If you must keep the speakers, Creek CDP and amps are voiced well for Epos, all being from Mike Creek's company, and this is the best I heard from Epos.

Other option is to buy an equalizer.