Thanks for everyone's help, much obliged!
What I had in mind was building the sub towers as a single unit per channel, i.e.,
like two 12" triples, but attached, (like an Ikea Expedit)..., with six 12" drivers per channel.
I would then use these doubled cabs as speaker stands for my active monitors, the Oceanway HR4's.
Q: Can all the drivers face forward, or should they be staggered Front and Rear, say, in this pattern:
F R F R
R F R F
F R F R
(L Ch) (R Ch)
Also, it would seem logical to employ two A370-XLR2 amps per channel, one amp per three drivers, (the 16 ohm drivers)
which would allow me to run the signal balanced from my preamp, to the Master amp,
then jump to the second A370-XLR2 as the "Slave" amp.