Thank you for your kind words, imdoc! I enjoyed talking with you very much. One thing I forgot to mention - you’ll probably have to EQ in a fair amount of low-end boost in your room. I suspect that the big opening behind the listening area is acting sort of like a bass trap and reducing your in-room bass. You might also experiment with putting the two subs in phase quadrature (90 degrees apart) - it may be beneficial.
Tim, if you look up imdoc’s system (just click on his name), you’ll see a photo of his room. It is a beautiful space that is not a dedicated audio room, and in my opinion multiple subs distributed around the room would ruin the aesthetic he has achieved.
The room is open at the end that’s "behind your back" from where the photo is taken, so that room dimension is not distinct. The other room dimensions (width and height) don’t support room modes below 30 Hz, and he’s only looking to augment the Maggies south of 30 Hz, so the net value of the modal-region-smoothing we get from a distributed multi-sub system doesn’t apply as much. In this situation, I think the more cost-effective and aesthetically practical solution would be two high-output subs that fit in the areas behind his Maggies.
At first I was thinking that a pair of tall two-woofer subs dimensioned to fit behind the Maggies (and shaped to be Maggie-backwave-friendly) might work well, as with one woofer high and one low, we’d at least have our bass sources distributed in two dimensions (height and width). But then I thought about his room dimensions and the modes those dimensions would support and decided that the benefits would be minor, and that it would be more cost-effective for imdoc to just get two powerful conventional subs rather than paying to have expensive custom enclosures built. So I suggested he look at Rhythmik, though they are by no means the only viable choice out there.
Duke