With all of that in mind, I may try implementing the flanking subs again when I install the center channel. If I do, could I check for proper integration using a measurement with REW from the main listening position? Sounds like I'd be looking for a relatively flat response at 100hz, and fewer peaks and nulls below that compared to the 3Pi on its own- correct?
I also had a thought: I'm using a miniDSP for the sub crossover and volume, and could easily implement a delay with respect to the main speakers- could that be used to approximate moving the subs back and beside the mains, or does that just open another can of worms?