Acoustics experts - a little help please

Setting expectations straight, 3D is a foolish concept concept in purist stereo.

A BACCH processor will trick and give some semblance of 3D in a stereo rig.

You will need a multichannel rig with ceiling speakers, back speakers etc and object based audio processors for true 3D.

But, if you turn everything loud enough with the stereo and everything’s smacking the face left and right, it could help you not think about (obsess about) 3D. These type of obsessions tend to occur at low listening levels.

Having said that, hang 6 inch traps (absorption) right above your listening position with an air gap like what @mashif  did.

It will mitigate the impact of standing waves/modal issues heightwise. 

(Floor and ceiling are parallel surfaces)

I have 9 foot ceilings and I sit in a 9 foot equilateral triangle with my speakers. Do I need to treat the ceiling?

Maybe 3D is the wrong word. I'm looking for soundstage depth. Paul McGowan talks about it in one of his YouTube videos. Apparently in his setup you can hear images left, right, center and 5 feet back, 10 feet back, 20 feet back, etc. Appreciate the advice! 

The best soundstage depth I ever heard was 3" single driver in large TL cabinet and Wavac SET amps. Yes, depth was 10’ back or more. Song must be appropriate and one was Michael Jackson’s song with footsteps in it - maybe Thriller.

His room was huge. Maybe 20’ x 30’ and speakers way out into the room. Wall behind was maybe 15 feet back.

The large room, speaker position, along with phase and time coherent speaker were the keys. The first and easiest step would be maximize distance behind the speakers. Not sure of treatment behind the speakers would work. That absorbs reflections.

Room acoustics is a complex matter...

 I had no experience as a serious acoustician in many room with many different problems...

 I know how to learn what we need to solve a specific problem in a specific room...

 Consulting a serious acoustician will help you...

Or do as i did but it takes much time so much most did not have the luxury to do it ...Read articles, books, and do your own experiment in your room...It was the best fun in my life...

I cannot advise you without being myself in the room and experimenting...I did it mechanically with my ears...

 A pro acoustician can give advice very useful for your specific problems...

 The best soundstage i heard was mine in my first dedicated room, but the tuning takes me 2 years...

 I apologize to be of so little concrete help....

Looks like you need sidewalls and ceiling treatment. Front wall treatments don't really do much to control early reflections, as these are the ones that need the most attention.