Has Anyone Ever Run TWO Identical Pairs of Speakers ?

you are talking about an old thing people used to do
 one example is Quad   many others also  Now we have   MTM  type speakers
  I would not go looking for any  unless you trip over a pair you like     

Fiesta, it is not theory. It is solid acoustic management. Yes, I have done it. I have two pair of Mirage speaker in my workshop. I got them in 1987 as stop gap speakers while I was waiting for my Apogee Divas to be made.  I tried stacking them one on top of the other with the top speakers upside down trying to get the tweeters as close together as possible. It went plenty loud. Low bass was missing and the imaging was vague. To get more midrange power a D'Appolito array is the best way to go if you have a strong enough tweeter. You could do a linear array of tweeters stacking small tweeters in a vertical line ala Pipe Dreams otherwise a single tweeter is always best which is why so many very expensive speakers do just that like Magico, Wilson and YG. This is my chief argument with Tekton speakers. Tweeter arrays like they use may get cheap tweeters to go loud but imaging goes right down the tubes. They might pay $2.50  for each one vs $300 to $400 for real tweeters. Real speaker designers are laughing their a---- off. You have already seen multiple Tekton buyers relating that they are very unhappy with the purchase. 

I'm certainly not saying multiple tweeters are the way to go, in fact I like both vertical and horizontal driver alignment best. Just said sometimes the benefit outweighs the imaging issue, like volume when I was still in college.

I have 2 pairs of HPM-900's  identical in every way, even the re-capped x-overs are the same. So I tried the side by side method, not a very good outcome, but when I tried the vertical stack I was impressed, kinda like 2 big PA stacks at a concert, sort of a wall of sound if you will.

Actually, ran 3 pairs of inexpensive Pioneer bookshelves...hung in my shop for something to drown out the saws, routers, sanders.  'Low rent concert stacks'....vertical, natch...

An improvement on what they were, until the guys blew one of them in a fit of enthusiasm.

Going to knock them down to 2 pairs and add a CV I’ve been gifted with as a ersatz sub. It’s about what it’s worth doing with, anyway. ;)

Pretty much the same for the ’neers....*L*

Rude experiments in cheap audio; not ’phile, just tunes.