How much acoustic room treatment

I would experiment by removing the bass absorption, or relocating them to the opposite side of the room. 

Mark, 

What you describe points to something else at work, if you take off too much high freqencies then the midrange would be more prominent and should sound warmer,  if you are now finding the midrange is now too sterile you are not just damping the room you are sucking out way too much energy.

All acoustic panels are not the same, we hate fiberglass based panels because they tend to do what you are talking about,

You want a broad based panel which has both absorption as well as diffusion.

First step is removing all the panels and adding them in slowley and trying them in different places and looking for a neutral tonal balance.

Which panels did you purchase?

Dave and Troy
Audio Doctor NJ

https://www.acousticalsurfaces.com/sound_silencer/sswall_panel.htm

we use these panels to construct the sound  proofing for Rev Runs Theater as seen in DIY Rev Runs Renovation. 

We also used these same panels in our theater. 

Bass traps ASC tube traps. 

The above panels material is both an absorber and a diffusor.

You would want a quadratic or 3d absorber panel for the rear wall.

PM us for more details if we can assit you.

Dave and Troy
Audio Doctor NJ

Too bad you have to ruin the walls in your home using adhesive with the Acoustical Surfaces.