Single vs. Dual Subs

Recently blew a sub in the living room where I run a two sub system for video.  Decided to move the matching sub from my listening room there and replace the listening room sub with something newer.  New Martin Logan 800 X (10" sub) to augment the 8" woofers in my classic Acoustats is working beautifully.  Everything adjusts from a phone app at your listening position and it has Anthem Room Correction built in as well.  Sub is tucked away behind the couch wood arm at the far right.  It's gets lots of reinforcement coming out of that couch  "baffled" corner.   https://www.martindareff.com/Other/HDR-Treated-Images/i-3ZfL6Gq/A

Using a Dual Rel T7i subs make my soundstage become wider and deeper, comparing to one subs only. Also, the bass goes deeper and smoother. I am not a scientist, so I don't know how to explain it, I can only report what I observe. Also, placing the dual subs right next to the speakers closer to the side wall makes the soundstage wider, comparing to closer toward the center .

I ran a single powered sub (15" driver) for awhile in my main listening room and then added a second.  The second made a considerable difference to the sound.

Save yourself a lot of time and effort and go directly to a Swarm.
I just set mine up two days ago and it was an epiphany.
All my bass issues were resolved immediately. Smooth, balanced, realistic low end. Now it's time to tweak things.
Very simple.  I used a MiniDSP 2x4 connected to the pre outs on my integrated, set the parameters in the software, then connected the outputs to 4 subs (two REL, one SVS and an older Sunfire). Only downside is more wires running everywhere and five more power cables. 

Pray, do tell us all.
Integrated model and connections, Main speakers, room dimensions, DSP parameters, sub models & location