Absorption, Diffusion or a combination of it all?

You can reach out to GIK directly and they will do an assessment of your listening environment. GIK has an online form that you fill out and you can include photos of your room. I had tried doing it on my own, by tackling first reflection points. But when the analysis came back one of their techs came back with a detailed analysis and set of recommendations that included some of the things I had and then went further, like a pair of 4A Alphas Series Bass Trap Diffusor/Absorber -- which are amazing! -- that go "on" the front wall, behind the speakers (though not directly behind.)

Anyhow, to me, that is the way to go. Reach out to them and see what an expert says.

Does GIK really do an assessment of your listening environment?  I modeled my room on their site, uploaded photos of my room, and uploaded REW measurements.  All I got was a generic response that did not include anything related to the specifics of my room.

@Gordon

Yes, that was my experience. Mike Major was the guy that helped me. I submitted all my stuff. He replied right away that he was stacked up and would need some time to review. (I liked that b/c he set the expectation up front.) He wrote a fairly lengthy set of recommendations and comments. I was impressed.

I wouldn't have posted if I wasn't so pleased.

Maybe you could try again and/or call them.

As with everything else in this hobby, it takes a lot of experimentation to get the best results. You can get a head start by hiring an experienced acoustician to come an evaluate your room and provide recommendations, but your personal tastes need to dictate the final solution. 

It's relatively easy and inexpensive to experiment with absorption since low cost fiberglass or rock wool panels can be purchased from your local home-improvement store (Lowes, Home Depot, etc.), or you can just use spare blankets, pillows, quilts, etc. 

Diffusion is a bit more challenging since good diffusors are somewhat costly. I haven't found the cheap diffusor panels to be that effective.

But once you get it reasonably dialed in, acoustic treatments provide a LOT of bang for the buck. 

I got an email chain going with Mike Major of GIK. His recommendation based on information and pictures I provided is to fill the side walls up with at least 5” thick absorption panels all the way to the level of listening chair and go as thick as possible with bass traps on the front wall. 
 

I’m evaluating all suggestions at this point as I continue the researching.