Yet another Sub Question

Your stated main speaker response isn't digging very deep so the sub will have to reach up a bit to cover the mains.  This being the case, I would expect that a two sub setup will blend much better and produce fewer and less aggressive nodes.  If your mains were rock solid down to 35hz one sub covering the bottom octave 20-40hz might get it done but that's not your reality.  It would be ideal to get a dealer demo loaner to play with your existing sub to see how the pair works in your space.  Good luck and cheers

Get a second T/9x.  It does exactly what @ghdprentice says.  Soundstage extends in all directions and imaging improves.   I’m not aware of software for setting up a REL.  Neither of my T/5xes came with software, but they do have good videos on setup and integration.  My pair was relatively easy to get sorted.

what does the REL website speaker pairing suggest? If it says some s/510’s are the answer, then it’s a matter of getting the girl and then save for her twin sister. 👧 👧. 

A single sub can work great for a single listening position, otherwise lots of potential room problems...I bought a single larger REL, then another a year later...single sounded fine, but two was a very nice improvement...

what does the REL website speaker pairing suggest?

9x

Well the REL site does not have my QUAD Z-4.  But the Z-4 are in the same class as say Focal 936 or 948.  I had the 926 prior to the Z-4.    All the Focal Aria series result in a 9x suggestion for my room size.   Thats how I ended up with one.