@Triodes4ever, we are going to have to insist that you post some pictures of your experiment. Otherwise it did not happen... LOL!
I experienced pretty much the same thing you are describing with an early attempt at a 2-way Cornscala using the K-510 and CS500 crossover.
Everything that the good people above have noted are factors preventing what SHOULD be an incredible speaker from sounding like an incredible speaker.
One of the issues preventing the sound that those drivers are capable of producing from being received by our ears is the response curve of the (any) HF driver. It is easily 10db more than the woofer and drops off as it goes up. Couple this to the horn lens and the curve becomes more pronounced.
As has been suggested either the highs must be boosted, or the mids attenuated. An equalizer would work, BUT the cat’s meow for this would be an active crossover.
Failing that a more specific passive could be built. From where I sit, a slightly higher crossover point, some (much) midrange attenuation and a steeper slope would be a game changer. Not as much as an active crossover though, as it would time align the drivers AND allow for very specific PEQ’s to fine tune the end result of the drivers, horns, and cabinet used.
Having said all that, I still have not hooked up my Ashly Protea 3.6, sigh...
I did however luck into a previously unknown-to-me (and probably most others) passive made by Bob Crites for the Faital HF200 and the larger K-402 horn. It does in fact cut the mids, resulting in the highs we both know were in there reaching our ear-bones.
All of this was right about the time LaScalas and folded horn bass bins changed my life so the direct radiator approach to music has very much paled for the foreseeable future.
The K-510’s and Faital HF200’s presently reside, manually time aligned, on top of Peavey FH-1 bass bins with Kappa 15C’s and Bob’s “B&K Belle Passive for K402 w/Faital Pro HF200” crossovers.
Good luck with your equalization curve, whether it be active or passive.
...those Cornwall IV’s are lookin’ pretty sweet about now, lol