What affects front to back depth in room/ system?

Your perception of depth of soundstage is most likely negatively impacted by the first reflections (side walls, ceiling). Also, adding bass traps will help solidify the soundstage. When your brain needs to process sounds bouncing off every reflective surface, it will have a tough time realizing the stereo image. 
Easy way to test it is at very low volume where the reflections are minimal, does the depth increase?

Let's consider some of the basics of perceived soundstage depth.  Sounds that seem way behind the speakers have reverberation which is either natural--from distant-miking--or artificial.  Sounds that emanate from the plane of the speakers are typically close-miked without much reverb.  To have sounds in front of the speakers in a stereo system would require that the phase was reversed.  Or maybe it can be done with a surround system.

With regard to southern California dealers, I thought Alma Audio in San Diego did a nice job of setting up their Boenicke W8 speakers to create a sense of depth. The sound was very enveloping. Nice looking speakers that sound excellent, imo.

@veerossi adding to my earlier post. Now that I saw your system….very nice! But I’m afraid, in addition to room acoustics, lack of preamp is contributing to the soundstage limitations you’re experiencing. 

It sounds like I need to finally get going on my room treatment. I’m not sure there’s much left for improving speaker position in the room. My speakers dissapear 90% of the time right now. I need to finally buckle down and learn how to use REW.

Earlier I spun the Mofi Brothers in Arms and on "So Far Away From Me" I get the sound wrapping around the room- almost like it’s giving me a hug. My thought is: somewhere there’s a treated room with a properly setup system that can do this full-time. I’m holding on to this as a goal.

Not seen in my photo is the rest of the gear that’s against the back wall. I will try going back to the short wall for the setup, but will need to muster up the energy for that chore first.

@8th-note The BSG QOL Processor sounds interesting. Do you recall how much it cost?

@o_holter One of these days, I need to hear Quads. For a long time, I’ve heard so many great things about them.

@testrun Wow, that Moon River is a spectacular recording. It's ASMRish! Soundstage is massive!

@audphile1 The depth doesn’t change much at low volume, but I can tell when I’m at the right volume. There is a volume where the pressure in the room is just right. Too little and it’s a bit dull. Too loud and it overwhelms/ excites the room. Using my phone and the DecibelX app, around 70-75db works well.