Y’all are fretting a bit much... 
If i wanted a flat line just to please Amir/Erin, i could have just diy’d/built out a GR Research NX-otica or NX-Extreme on the cheap......and lived with over the counter lower quality drivers. It would sound fine and show y’all a flat line, for sure...Or get some sterile monitor.. Last i recall, every magnepan i had measured like true hiny, but i always loved the sound of it, etc
I never had this X3 ( i see 1 issue that’s relativley harder to fix, doable though)......But, i acquired the X6 used for 10k from a trust fund dude who seems to shed speakers quicker than socks, a deal i couldn’t refuse, couldn’t say no...no brainer for me. Will i sell my X6 with how its sounding? Hell, no...for the following reasons.
I had a plan...I wanted those high quality Borresen drivers and driver count, that I couldn’t just buy off the shelf, a speaker with good bones for playing with. I wanted those ’small’ drivers with the impulse response i need to carry through up to ~2.5khz before handoff to the ribbon. Cabinet has my preferred aesthetic and volume + finish i needed.
I have a custom crossover mod that i run with the tweeter level dropped lower (quite easy to do) and a slight bump about 2 db higher ~1k onwards before tweeter hand off for the spatial qualities i desire. This is very hard to otherwise find with the sheer cluster of flat hiny or bbc dip/trough speakers out there. Further, I have a low Q ~3db bump from ~80 to 250hz and Kef KC62 subs dovetailed on the low end getting down below 20 hz. At the end of it, no flat line but smooth low Q bumps exactly where i want it, just the way i like it...my modded X6 sounds like a less dark, spatially enhanced high clartity/resolution/detail version of a Pioneer S-1EX perhaps that cross-bred with a magnepan or something.. or if i almost turned on atmos at times, quite enjoyable i say. Maybe someday, i’ll go fully active with it or not.
I am sure if Michael Borresen wanted to give y’all a flatass line, he could do that in 30 mins. He has some hangup about not introducing a electrical phase shift with the bass/mid handover, whatever. Maybe, he was also trying to do something with this X3 as a ’lifestyle’ product as well, i.e., his majority market will put it in a living room or some suboptimal room modal hell, dinosaurs who refuse to use a sub, no treatment, etc where none of this mattered anyways.....
I mean... you could take my other speaker, a pristine measuring TAD, put it in some untreated living room modal hell, measure at your listening position and see what you get..keep looking for the long lost flat line boys.
Either way...don’t know...don’t care what exactly Borresen dude’s philosophy is.
P.S.
I actually run the X6 on very modestly priced electronics from Schiit. It never got "carried" by high end electronics and sounds like a million bucks.