Thoughts Please - Rear in-wall acoustic treatment

Hi All,

Looking for your thoughts.

I am doing some reno's which has required the removal of the gyprock on my rear listening room wall.  Photos attached.

Whilst the wall is open, I am wondering if I should put some treatments in the wall, and if so what ?  

My goal is sound quality, not sound proofing.  I am good to remove rest of by-rock as well. 

As an fyi, I do have absorbers on front this wall behind the listening position (red couch in photo).  Other side of the wall is a bathroom with tiles on wall.  Listening room has acoustic underlay, think cut pile carpet, and acoustic bumpf in the drapes.  I believe I have tuned the room reasonably well.  RTA60 photo attached.  Room is both music and home theatre.   

Value your thoughts.

Many thanks.