Hi guys, I recently moved and it's taking a while to get everything settled. I prewired for 9 speakers and 4 subwoofers. I'm going to be running either my BP8's or a pair of PM1000's L & R, my PC2000 center, BP1.2x's SL & SR.
I'm only running two of the four subs right now as I'm waiting for a product called miniDsp to arrive from overseas. I plan on using it to manage my 4 subs as Audyssey Multi-EQ my denon 1909 only manages a single sub. I plan on posting REW measurements to share any benefit I get from using single/dual/quad subs in my room which is a typical living room in so that it is not a dedicated listening space, but is open to the rest of the house.
I took this picture just being silly. Two of the subs are in the back of the room currently.

I was super disappointed with the bass running two of the subs on either side of the stand. It was horrible: weak and muddy. Turned out putting either one 180 degrees out of phase with the other tightened up the bass notes and output increased significantly!
I had the builder leave the wire behind the drywall so I could decide on speaker use and placement after listening in the finished space. I have my BP1.2x's 7 feet above the floor in the back of the room and so far they sound really good after some limited listening. Before I add terminals to the back wall for PM1000's SBL & SBR, I will put them on a couple of ladders and listen to them to see if they make a real contribution.

I hope some find this helpful or interesting and will report back when I get things settled.