Yeah, I would assume that integration would be an issue, but I have to think that the guys building these crazy systems have considered that and perhaps how to get around it without necessarily resorting to DSP. I personally find pin-point stereo imaging to be fairly low on my list of most important sonic attributes, so that probably wouldn't be of concern for me.
I'm curious if this could be solved, in part, with simplifying these systems to 2 or 3 way drivers where the low frequencies are separate, but mids and highs are driven by a single (or 2 driver for a system using super tweeters) full range driver that uses a single huge horn. Admittedly, I do not know enough about the engineering here, but I have to think the guys building these types of huge custom systems are thinking about solving these integration issues in a way that horn builders looking to sell via retail channels simply can't do. I'm curious how they've done it and how successfully it has been accomplished in some of these very different custom approaches.
I've spent years developing such a speaker and it's almost ready to go!
The horn is not conventional. It has enough gain to linearize the 4.5" driver it uses in the frequency range it needs it, so the horn and driver really need to be co-developed. They are an inseparable unit and this also determines you crossover points. So the entire thing needs to be designed right from conception, you can't "mess around" with xo points, etc... it's basically set in stone. The horn also needs to be designed appropriately so it can cover an extended frequency range, and this is where everything about conventional horn design goes out the window, not that it didn't before with the horn significantly altering the driver's frequency response while leaving it's high frequency response unaltered... In any case the horn covers 400-15000 Hz. A Fostex T500MkII augments the highs and a 15" Acoustic Elegance TD15H+ covers <400 Hz.
This also makes integration very easy, in fact you can listen to my speaker nearfield like a singe driver. You don't have a massive mismatch in mechanical impedance between drivers either, like you do with conventional high efficiency horns combined with direct radiator bass. Overall efficiency of the mid/high section (>400 Hz) is ~102 dB and xo is a single cap on the mid driver and tweeter, so a mid/small SET amp works great as long as it has enough gain.
One of my favorite things is that it lacks a dome or ribbon tweeter. IMO the highs are better than any conventional speaker, but I might be biased...
The speaker also has a near-ideal polar plot so it integrates with conventional living spaces very well, much better vs conventional speakers. Overall goal is to provide a 3-D immersive soundstage that conventional speakers rarely achieve, and do it in your living room... something conventional speakers almost never achieve.