I can't really vouch for the behringer gear, but i can the h-700.. I am using it with cd-2 mylar's, morel mids and max subs so i am kinda familiar with what your doing...I have to say though, there is no way possible that a 4 or 5 will keep up with the horns unless you can 10x the power....10w to horn and 100w to mid..seriously....although I am doing a 2 way front and not 3, and the morel's are somewhat inefficient, unless you do a pro mid like phl, b&c or the sorts, audax has a nice one i hear, you will have a hard time with running 30+ watts to the horns. I am still debating on running a 3 way front myself, but if you are going 3 way, I would do a 8-6-horn...keep your 8's at 150-200 and lower and mids from 150-200 on low side and and 1k-1.4k if mini's or 600ish to 1k if full...
another thing you have to look in to, not too many processors out there that will do a true 4 way setup...dual bandpass abilities I mean...if you do find that, by the time you get everything that the h-700 can do, your in the same boat $ wise...I don't hear these noise issues that people are talking about but I am running ainet from a 9815 too and not running rca's to the brain like some are with a different brand source...if you use another brand head, I would find one with a digital out and use the controller for volume....your head will be dead (transport only) if you don't use alpine..
good luck in your quest though man...once you go the horn route, it opens a whole new can of worms imo personally....staging is out of this world