Sometimes I wonder if you guys have been intercepting my e-mail communications. 
OK yeah well I've been driving over from Bonham, Tx to Iowa Park and intercepting your wi-fi.
Didn't you see the van on the street? ..... Sorry never been there and don't own a van.

This is a design that has always been of interest to me and I've got a speaker now that's
supposed to do that now, but didn't build it because the guy that sold it to me has abandonded
DIY for finished speakers. I insist that whatever I use and recommend has to be kit. Otherwise
I would have gone PMC or Meyers for these monitors a long time ago.
What about a base speaker without the sub that maybe doesn't have to be a swiss army knife
for all rooms? Let the builder handle the subs and integration but give them the killer performance
from 200Hz up. That's really what I was hinting at. For reference monitoring, imagining and performance
above a couple hundred Hz is where it is at anyway. BTW I've been using some IL-60s for over 10
years that are set up kind of like what your describing and they work well and are great speakers
but not for recording work.
Also maybe make the amplifier requirments a little more rigid, like an Aragon (which I use) or
Bryston or something like that. Something that could allow the speaker to be a kit.
I guess kit is kind of a major factor to me. That's being said what is the target retail price
for this contract speaker you're doing?