So one gets 1.4"-2" drivers that have a nearly planar wavefront or correctly curved wavefront at the throat to enter into a (presumably, or at least in one direction) narrow dispersion horn. Any suggestions as to suitable drivers? (The BMS 4550 is known to be a very, very efficient driver that can be crossed very low for instance and outperforms for eg the B&C DE700 acording to some German designers but you have commented in response to Tom Danley somewhere that they don't strike you as suitable)

3 large format compression drivers per cabinett would be some very narrow dispersion waveguide like in a line-array presumably?