Room Treatment? How important is it to treat the wall behind/between the speakers?

2 or 3 of these on the front wall would help, but again it depends on if the room is too reflective. Usually this works best. https://www.gikacoustics.com/product/q7d-diffuser/?tw_source=google&tw_adid=649245158855&tw_campaign=19732823023&tw_kwdid=aud-1960089553334:pla-293946777986&gad_source=1&gad_campaignid=19732823023&gbraid=0AAAAAD-4A3F6gAISH72YM8xitFwA92Cxa&gclid=CjwKCAjwlOrFBhBaEiwAw4bYDZk2xlwzmWaT1Na8GDPm5bucLMq9R8Y4X4U1S3FVhkGfH8u-somATRoCPzgQAvD_BwE

The recommendations from both GIK and ATS were consistent when I requested assistance.  Diffusive panels directly behind the speakers.  Bass absorbers in the corners.  Both companies reviewed my room and setup.   Both indicated I did not need diffusive panels because my wall unit was sufficiently textured.  I recommend you contact both and send pictures of your room and set up and follow their recommendations.  

@macg19,

Your equipment is very nice and room seems to have good capability. First thing I would do is to move your speaker at least 3 more feet into the room (if possible). Adjust the seat position to close to an equilateral triangle, keeping all vertices between the speakers and speakers and you the same. That will also improve direct sound from them vs room reflections. I use lots of diffusion in my room (all walls and ceiling). You can check the pictures of my room in my profile. They are not updated after my latest diffusers and bass traps inside the closet were added, but you'll have an idea. Best of luck, 

Thank you all for the advice. I could move the diffusers on the left side wall to the front wall and use an absorption panel instead. The right wall (bay window) already has an absorption panel + drapes. 

@kellerjr01 Thanks! I have tried the speakers 5ft from the front wall but the bass gets boomy + it puts the listening position too far into the living room.

I plan to add something like the GIK Soffit Bass Traps floor-to-ceiling eventually but there are other priorities for $$$ atm. 

My understanding re: diffusion panels is that  their effectiveness depends upon the size of one's room since they're not helpful in small ones. As to what constitutes a small room...GIK and other experts can guide you. Good luck!