can subwoofers make things worse?

I have two Rel T/7i subs to supplement my Sf Olympica III’s and hear the same benefits as @jastralfu describes, albeit in a slightly larger room (16’w, 22’l, 10’h) -- the soundstage, imaging and presence (the apparent size of each instrument and player) was nicely enhanced and made more musical with the addition of the two Rel’s. The addition of the second Rel definately improved those sonic elements over my previous SLF850 sub (a 10") by itself and combined with the first T/7i. I set the crossovers at about 60db and the volume a little below 3 out of ten or 9 o’clock on a standard dial. This seems to work just fine for me, the subs do not call attention to themselves, the music seems to come from the Sf’s only.

It's not the quality of a sub that will really degrade the sound, it's the position, extension and whether or not you can clip excess peaks.

I recently added two Rel T9x, Klipschorns, 13'W x30'Lx9'h room. didn't really add much bass. but expansion in sound staging far surpassed my expectations. I've spent much more on electronics in the past and never experienced this level of expansion, should have done this years ago!

T series Rel's don't reach lowest freq in bass, but I've never experienced this kind  of coherence, integration with other subs, and those with dsp. With other subs constantly fine tuning sub settings with different recordings and volume levels such that it drove me nuts, gave up on subs for years.

I suspect two smaller T series would be seamless integration with your setup, as others have mentioned a single sub more difficult.  Smaller T series won't overload your room with deep bass and should provide very nice expansion of sound stage.

Doubt a sub or two will make things worse, but you have to take the time to find out where they sound best.  I currently am only using one and it’s six feet behind the listening position and only does sounds below 45hz.  You will have to figure where it rolls in and how fast the slope is. Mine is set at 12dbs, I believe and how much volume you want from it etc.

All the best.

I have two SVS micro subs, one sitting beside each of my powered monitors. It sounds well integrated and tight. The room (open floor plan) is 16’ x 24’ with openings all around. 
 

I’m probably a minority here, but I don’t want to see my stereo, at all. If I could buy an invisible stereo I would. So, not that the micros miss anything, but they are as big as I want in the room, and it’s a close call with them. 
 

The phone app is very useful, fyi, and two subs seem much easier to integrate compared to a single sub. SVS has a pretty good shipping and return policy if you are tempted to give it a whirl.  Check out the website. 
 

Hope this helps, best of luck with it!