From this perspective, this horn looks huge (it's not really that big).  I made some more progress on the horn and devised a nice way to attach the driver cabinet to the horn through "wings."  I attached them with Festool Dominos for a really strong link.  This way, the driver chamber is fully detachable from the horn if I ever decide to swap the EV15Ls out for something else.  I took a lot of pictures of the build which I'll post when I get a chance.