Question: Sound Treatment behind the Listener?

@ozzy  makes sense I think. You have a decent size room so they’re recommending abfusors.
FWIW, for my room, which is smaller, Mike recommended absorbers on the sides for early reflections and tri traps with range limiter in corners behind speakers. 

Thanks,

I'm not sure how many of the Alpha 6a's would need to be acquired. 3 of them with shipping is $763.

ozzy

I use Rockwool @ 35Kg per M3 floor to ceiling in height as a Absorption Room Corner conditioners. Directly behind and spanning between the Speakers I use a Diffusion Panel.

Each Side Wall has a diffusion pane.

The Rear Wall has a Aborption and Diffusion Panel set at a height of the listeners ears.

The sound is managed in a manner that has improved attraction with these measures in place.

Would it be identified as a accurate treatment using tools the can measure room modes is an unknown for me. 

Thanks Vinyl Shadow for the info.

I'm getting some advice from GIK but also just started a dialogue with Jeff at HD Acoustics who I found when searching here. It won't be free but it will (should?) be unbiased and sounds like he knows what he is talking about....because I don't w/ acoustic treatment on the rear wall.

I have found the Acoustic Insider channel on YouTube to be a good source of information around treating your room.  He mostly discusses treatment for small home studios, but the theory still applies to a listening room.  

As far as I can tell, he's not selling anything.  He does reference a document you can download, and I have no idea if he charges for it or if that is a gateway to purchase other stuff, but I've never looked into that.