Yet another Sub Question

Yeah I currently have the existing 9x set really low.  Don't take much and mud happens

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...