Subwoofer for music, how low?

+1 for distributed bass array

If going Tekton, might as well get a couple (or 4) 2-10 subs from Tekton and yep those do go down to 20hz - which is an important thing for a sub to do in my book.

Virtually no music is down in the 20-40 hz range and I doubt the t9 can really deliver there anyway. I have a REL S5/SHO and properly set up in an acoustically tight 13x 22 listening room it does a great job of delivering deep bass- when I measured there just isn't much music at those very deep levels. Most sub activity is in the 40-70 HZ rang or so. I'd go with a larger box and drivers which will provide deeper and louder bass than the T9. 

I have a Totem Thunder, with my Forests but just ordered a pair of SVS sb-1000 pro subs. I’m not in need of excessive bass, especially with the Forests that have a considerable amount of bass already. I wanted a matching pair to give flexibility in my small/medium size room. They have a sale going on right now, so I went with the pro series as it has an app for my phone that can control the many features of them. Nice to be able to control them without trying to “access” the controls.

If you can afford JL Audio, I would go with them. I’m utilizing mine with the Wilson Audio speakers and the Wilson Crossover. Easy to blend in the room and you don’t get wasted sloppy bass. It is very precise and accurate down to 20hz if any of your listing music goes that low. One of the best subwoofers around and a great reputation too boot.

I am also utilizing 4 JL Audio Subs. 2 Fathom 113’s and 2 Fathom 110’s