What process did you use to integrate multiple subwoofers for 2 channel listening?

Today I will be trying to integrate up to three subs. Two are matching Rythmiks F12SE, and one is a REL R-328. The Rythmiks have a variety of adjustable parameters, including phase, crossover, and gain. There are other switches and passes on the sub, but I'm going to try to keep it basic to begin with. The REL has variable gain and crossover; the phase on REL is either 0 or 180.

I have REW for measurement. I will be buying a few more furniture sliders this morning, on doctors orders. ;-)

QUESTION: If you have multiple subs, by what process did you integrate your subs? One at a time? More? Which adjustments did you try first and in what kinds of increment?

I know that trial, error, measuring, and listening will all take time. Rather than look for a needle in a haystack, I'm curious what sequence or process was most effective for you.

Thank you.
Not to many speakers do full range. The JTR Noesis 215RT is one perhaps some of the big JBL cinema 3 ,4 or 5 ways. They still would need DSP in my opinion.
All the speakers have their own power amps, so it is quad amped with an electronic crossover.  that makes it easy.  My subs go for like 70 to 30 Hz, using the Klipschorns.  Then there are the sub-subs, each having 4x15" in a tuned quarter wave huge tube and a 1KW plate amp.  Three of those on separate power.  Obviously these are different, as they are FLAT to 4 HZ.  and the SOUND level, well it's more for show, no meter can measure so with the earthquakes I've been it, it appears R5.2. and yes, things move around, neighbors seek safety and all that. 
WOW, is all that I can say!

FLAT to 4 HZ, that is one Hell of a system, that obviously an be FELT & HEARD!

Just, what Maximum  DB level do you measure with your system?

kellyp - I'm not disputing, but HOW do you know it's FLAT to 4Hz.? Could you please briefly explain? So if my calculations are correct; one full 4Hz. wave is 286.96 feet, 1/4 wavelength is 71.74 feet, correct?