Thank you, actually I have seen those but was confused and thought those were HD, or Ryan's.
Also, confused because I first thought you had two front subs and two rear subs and you connected the FL, RL with a Y and FR, RR with another Y, but later you said that was your old setup and now you have only 1 rear sub.
Anyway, from what I can see in those pictures, the room does not seem to be large, but more like medium, by THX standard. Just eyeballing without knowing the dimensions LXWXH.
One thing for sure, worth repeating is that based on Audyssey's recommendations, you should always Y connect the equidistance (to your MMP) subs, so in this case, the FL and FR together, and RL, RR together.
If I got it right, you now have the distances and volume finally sorted up, so congrats, and time to focus on actually enjoying such a nice setup that should be great for movies, even serious two channel music listening.