A deeper more holographic soundstage.

A lot of random noise here. If you are happy with your gear and want to achieve a 3D Holographic Soundstage with scale and accurate instrument voicing, call Joe Abrams at Equus Audio. I’ve used MIT products since the late 90’s with excellent results. The new REV line Joe offers are extremely good and worth every dollar...they will allow your system to produce the most accurate rendering of an acoustic space possible.

besides room treatment the next important step is to get your digital equipment on vibration control gear. One example, my transport sits on TR bases from marigo, then his special shelf, marigo 4 40 millimeter vibration spacers, a granit mdf shelf, 4 six in. springs under that, and then another granit mdf shelf and then the final footers some kind of ball bering mini devices under that. Not only are taking out vibrations from your equipment but you are also dealing with earth vibration.I did this over ten years ago. More analog, three dimensional, cleaner sound than I ever thought possible. Vibration vibration vibration. This is the key to better sound.

Marigo audio is one of the kings of vibration control. Give him a call, he will help you greatly.

Look into BACCH4Mac or HAF digital signal processing.
I have no experience with HAF, but am using the BACCH4Mac Intro edition and probably will upgrade to the Audiophile edition (although it is rather expensive.) BACCH is a product of an acoustic research lab at Princeton University.

BACCH minimizes/eliminates crosstalk, manipulates the signal in the time domain, and can create rather dramatic effects on soundstage/imaging.  I'm told that effects from the more sophisticated ($) versions, "Audiophile" and up, can be breathtaking.  My own experience is that more magic occurs on some recordings than others. 
You won't hear much difference on, say, a Diana Krall recording (where all the attention is on one center image). But on one binaural recording, the apparent position of a trombone moved from at/near my left speaker to about 2 meters to the left of the same speaker.  Not only the speakers seem to disappear, but the walls of the house can seem to disappear.  It can increase the apparent depth and reverb. It does all this allegedly with no impact on the tonality (it is not the same in effect as room correction software or an old school graphic equalizer).

I have highly directive, hybrid electrostatic speakers.  These seem to work better with BACCH than some other speakers, so YMMV.  There is a 2 week trial of the Intro edition (and it's just software, so if you are not happy with it you don't have to ship anything back).

So, while room treatment may help and equipment rack placement may help, you can get to this level of imaging without it.

Interesting... I believe you because all room are different and dont need the same level of treatment, and some Audio system are already synergetically and by itself already very high S.Q. then i belive you...

BUT it is not true for most of people at all....In most case acoustical treatment and controls are necessary....Beside that except for lucky buyers, most very good system cost high price...

My speakers paid 50 bucks are very good but not on the level of your ATC for example...

But guess what, my S.Q. is probably near you, i listen to a soundstage holographic with perfect imaging, natural timbre with audible decay,bass i feel in my stomach, and the sound is filling my entire room at low volume ...Then all situation are different...Thanks to my homemade embeddings device... Without that compared to your ATC probably my speakers are way under in S.Q. term...

We cannot deduce that all costly system will be good without the need of any embeddings controls at all and will not need specific acoustical controls nor electrical or mechanical controls either...The general rule for most small room and audio system is they probably badly need all treatment and all possible controls...

By the way  i apologize to say that downright but you probably dont know what your own system is able to do more with a complete implementation of mechanical,electrical and acoustical controls...Perhaps your system even if you are satisfied is not working, unbeknownst to you, at his better level possible...

Most people unsatisfied or not, are not conscious at all of what are the really true high potential level of their audio system, what it is able to give when working in optimal controlled conditions... This is the ONLY experience and certainty i have acquire at the end of my journey...I called that embeddings controls in the 3 dimension of audio....

Happy New Year...