I really value this advice.
I too am looking into building 2 pairs of 4355 or 4350,s for a loft style party space
Having used Urei 813B,s for a while I really seem to be drawn to these type of JBL enclosures.. sure they're big, but for big rooms they seem to really hold their own. Solid.
They are beautifully simple and cost effective to build.. and with veneers they can get very nice
I keep going over options for drivers, amplification, processing,,, its fun to be inspired by all the designs and the sound of JBL