If using a DEQX, then you might as well by your speakers at K-Mart. :) Yea, I had one. Great for a PA system. Not HI-FI. Not even HT. The last thing I want to do to my stereo is add a $2 A2D and D2A in the chain with Op-Amps worse than 5558's and electrolytic caps even if the DSP was half decent. Now, setting up for a small band in some unknown club, I would not be without one. Never done a stadium so don't know about that.
I get the comments on very high sound pressure, but as I like my hearing to remain in tact, I do not consider that part of HI-FI. My humble stand mount 6 inch 2-ways can exceed permeant hearing damage thank you. One can do a DeApolitto MTM and reduce upper bass distortion at "Who concert" levels but at higher SPL, you can't hear the difference and if you play that loud, you just can't hear any more.
PA is of course a totally different animal where the problems of multiple driver comb filtering are overshadowed by getting the sound to the back of the room. ( Line arrays of those nice JBL's and compression horns) I don't think the markup is PA is as high as residential. Neither is fidelity. I agree, separate the adults from boys. Adults know better than to use PA systems in small rooms. We all did that as boys of course.
I also get what you are saying if you are replicating some ego-prestige all-in-the-name bragging rights like WAMM though I think you should look at that it takes to design and build such a monstrosity. ( I am not a fan having heard most of their line over the years starting with Watt/Puppies. ) But, do you think you can out-do ELAC on a D6.1? Can you equal a Dynaudio Special 40, Focal, Sonas Faber, Even a Kef R3? Size and price real people can pay?
Now we have increasing direct sales cutting out the importer, distributor and retail chain. ( we still pay that on components) So the equivalent cost is about half of the traditional chain. They do have to cover the cost of returns though. An example may be Taylor who puts together a seeming well worked out SB 2-way quite reasonably. If you want to touch entry level as cheap as possible, then a flat-pack CSS kit and a can of spray paint is far cheaper than even direct sales for similar quality and the design work is done. Just glue it together. Some of the Bagby or Zaph designed kits are not bad. GR has kits. I don't really consider a kit the same as DIY. It is just slapping together some one else's work.