Reading about the Meyer Sound Bluehorn in the MIX magazine article (installation at the Fox soundstage for film soundtrack mixing) made me think of the original early efforts to bring sound to film using large horns, eventually augmented by woofers since the "snail" shaped horns did not deliver much bass. The Bluehorn seems to be a modern answer to large scale reproduction, taking advantage of current technology--active speakers with dedicated amps, using DSP to correct time and phase differences, etc. If you consider how well regarded some of the antiquarian theater reproduction systems are today (WE, Klangfilm, JBL), these may be their more modern incarnation.
I did achieve a piece of this by combining the Avantgarde Duo with 15" subwoofers that use a relatively inexpensive outboard DSP system to flatten the response and got everything to gel the old fashioned way, through tuning by ear. But it's an unpredictable way to set up a system and it is obviously "tuned" to my preference in the room- not for perfectly flat response. And of course, much relies on the upstream equipment, all entirely tube based, utilizing expensive, hard to find old stock tubes.
I'm not suggesting one go this route. (I gather the Avantgarde Trio has the option of utilizing their built-in electronics and crossovers to accomplish room integration at a price).
There is something magical about the sound of a good horn system with SETs, though....