Shared living space always poses challenges to speaker/sub placement.
For music, what is missing? Those towers should punch quite a bit (for most music content at least)
For movies, yes a sub definitely makes sense.
Ask local FMs if you can borrow or at least try a sub into your rig.
You will get an idea of room interaction. Then make the decision on what to buy.
My story went a bit like what you are going thru now. The sub in my place is Onkyo SKW-320 (sealed dual 8"inch 100W).
I have IA with pre-outs; so hooked up L/R and added sub to the pre-outs.
Just could not get the setting right. So sub went into hibernation.
Then came AVR, but furniture hogged so much space that sub could not be placed at all.
Then AVR went into hibernation. Out came soundbar.
Now after simplifying and ripping apart furniture, I can host IA, AVR, power-amps, TV, center channel on a AV rack.
L/R are on speaker stands, leaving one corner for sub. Really that is the only corner available.
Hooked it up, let the AVR do it's calibration and that's it.
Movies it's 3.1 via AVR (sounds good enough for us and the listening space)
Music it's only L/R via IA (large-ish stand mount speakers)
The advantage I had was, components like center channel and sub were lying around unused at dad's place.
Pic of set up is here:
https://www.hifivision.com/threads/showcase-your-audio-video-setup-here.1167/post-807931
Cheers,
Raghu