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

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

Yes, I think you are on to something. I would seek out a pair of stand mount speakers and forgo the sub. I have used a pair of Esoteric MG-10s (2-way stand mounts) in a small room for years. Frequency limit is lower 40s. I listen to rock (not heavy metal), jazz, vocals, folk primarily. Don't miss a sub.