T9x would be great, maybe even the t7x. I had a rel s2 sho and it was too large for the totem arros that I was trying to pair it with. The reason I say this is because the sub would go from too quiet to too loud with 1 click of the volume control.
A pair is going to sound better too, so 2 T7x’s will be better than 1 T9x.
RELs are in deed “fast” which translates into being very articulate. I listen to a lot of music with low frequency information and I have not heard another sub that has the same articulation. RELs are also a sub bass system so you are slightly correct eith your assumption. From my experience, SVS subs that I have had, have more impact in the 60hz on up range.
You could look at SVS, Rythmik, and Velodyne as well.
if your dealer has a T9x on hand ask if you can demo it!