Am I Better Off With Limited Low Frequency Speaker In A Small Room?

You do have an issue in that you have a square room, which will create significant bass reinforcement issues. I had a similar issue with my floor standers that go down to 28Hz, and short of bass traps or DSP/room correction the only way I could somewhat alleviate the issue was to pull the speakers out 5’ from the front wall but there was still slightly overdone bass.

I would highly suggest going with monitors and incorporate two small subs that have their own integration software (i.e. SVS SB1000 Pro) that will let you better manage bass in your room and greatly improve your overall performance while giving you a true full-range system in the process — best of all worlds solution IMHO. I think you’re absolutely on the right track by also using GIK products and I would take their advice for your challenging situation very seriously as they really know their stuff. BTW, let us know if you need/want suggestions for speakers/subs if that might be helpful — lots of wisdom, experience, and hard-won knowledge here that may help you make more confident purchase decisions. Hope this helps, and best of luck.

I had a similar room and wanted to make my Thiel CS3.7 work in this room. I managed to do so with GIK and then DSP using ROON Convolution filters. Adding more GIK panels and moving reflective surfaces as far from the speakers as possible allowed me to eventually remove the Convolution filter. 

The sound was about 80% as good as the Thiel CS3.7 could do in a more spacious room. The speaker could not really breath but the sound as not fatiguing nor unpleasant, just not the best it could do.

I recently put in the KEF LS50 Meta with the KC62 sub and kept the GIK panels. The sound is fantastic, so much better than the bigger CS3.7.  The LS50 does not sound like it is being held back.

So I think putting a restricted low frequency speaker in a small room is the way to go. You can augment that with a great fast sub like the KC62 if you want more low end. 

I’d go with smaller limited range monitors and add sub or subs that you have more control over to fill in low end as needed. That is what I do in my 12x12 room. Kef ls50 metas + klipsch sw308 sub. Sound meter app to get a rough integration using streamed white noise then fine tuned by ear with music. Simple and Perfect! Two subs set up well always better than one but one alone to start may do it depending on how fussy you are.

I'm not a fan of subs. There can be a discontinuity in tonality. I have never heard one in a room where I didn't prefer listening to music without it. 

I don't need the extension if the speaker goes down to close to 40hz.

By the way, I have the living room setup at an angle to the corner to reduce parallel walls. 

Placement, tone controls and room treatment are your friends.  Use the AM acoustics room simulator to help you with placement of your sub and listening place.

https://amcoustics.com/tools/amroc