Acoustics experts - a little help please

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. 

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....

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.

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! 

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?

Certainly no expert, but measuring your RT60, reverberation time for your room will give you a start in which direction to proceed. 

Room is 30 x 18 x 9 

The room is actually 2 rooms joined. My music room and a dining room with a large opening between them. Essentially no left wall for the left speaker and the right wall is about 8 feet from the right speaker. There is a bany grand piano that helps with defraction of the right speaker. Floor is hardwood but I have a nice thick rug and pad under that. See system photos.  

@maprik  What are the other dimensions of your room?

It really depends on what is going on in your room.  If your speakers tend to run "hot" up top you may need absorption on the ceiling. If the speakers run dull or even warm, diffusion may get you there. 

I have 3 48x24x6 bass traps above my listening position. I plan to add diffusion above the speakers. It partly depends on your flooring. With carpet, the diffusion is more important but if you have hard floors the ceiling cloud helps a lot.