Installing subwoofers requires an even frequency response with limited decay to get tight bass. Multiple subs and feature sets included is subs are other tools to make this happen. With my limited experience I would suggest a larger subwoofer like the s812 or larger. I had an S510 with 15" main speaker woofers. While it was fine, it did not match the 'presence' and output of my speakers as well as my larger subs. 

@jl1ny

Sorry to interrupt but I am curious in what way is the S510 better than the T9. Room setup was the same for both models?

I agree that dynamic kick drum thump is doable without a sub (kick drums don’t go that low).

I was able to achieve this without subs by fixing the room and repositioning the rack on the side wall...nothing between the speakers but carpet. I also had a fantastic room at the time.

It’s not just the bass that hits hard, everything else comes into focus as well. I was able to achieve this with Salk Songtowers with 5" woofers. I no longer needed or wanted a sub. Funny thing is that I was not looking to improve bass...just trying to see what moving speakers to the other side of the room would do to imaging/clarity.

I would add the sub after you figure out optimum placement and room dynamics. I did it without software but it was a lot of trial and error over the span of a year.

The Tannoy 10" woofers in my current room could not touch the bass of the Songtowers 5" woofers in the old room.

So I ended up going with (2) 18 Eminence Tour Grade subs / BSS FDS 310 Crossed over at 80 , Crown Macro-tech 2400 powering the subs. Sounds super tight & focused and I have that concert level kick drum now...I can always ease in the subs or pull out as needed...very happy.