Pro Audio has been using multiband equalizers for years to tune theater venues. Recently, I spent $300.00 on a Behringer DEQ2496 and was surprised at how effective it was. Also corrected were some annoying peaks in my BG RD75 ribbon loudspeakers. The automated system took care of the upper ranges and I manually tamed some of the bass problems out. As far as I could hear the insertion of this excellant equipment had no detectable degrading effects. I am using the electronic crossover, Behringer DCX2496, as well with excellant results.
One thing that helps me with this 75 inch line array, is that the narrow dispersion of the upper band is not smearing intelligibility with strong wall reflections. I have the nacked ribbons with no baffle angled at 45 degrees from the corner of the room 16 feet wide that gives me a wall of sound presentation. Subs are crossed in at below 250Hz