The most important factor in soundstage imaging

Right on, tomic601!!!

@tomcarr.  disappointed YOU did not mention Jim Smiths most excellent book - Get Better Sound.

You turned me on to that :-]

and I thank you....

You guys are great!  I love all the knowledge shared on this site.  We have some seriously smart people here! 

I’ve always pulled my speakers far out from the walls but recently started really trying to tune / treat my room and it has done more for my imaging and soundstage than other one thing by itself.  

Before we get all technical, and deal with speaker design, placement and room treatment, the beginning, for me, is the recording. I have many different copies of the "same" record; some sound flat and lifeless, others have dimension. That's not the sole factor, of course, but for me, it's where it begins. Even with a good system, well set up in a room, a lackluster recording, mastering, etc. will sound very disappointing, particularly when compared to a better copy from a better source, better mastered, etc. All of the other elements in and relating to the system play their part, not necessarily in the order of the chain. Rolling a tube can make a difference in presentation. A phono cartridge change can make a profound difference (as can its set up). 
I don't have a holistic view of the entire picture to present in some logically ordered fashion of priority, but let's not forget the role that the source material plays in this process. 

Breakdown on imaging:

80%: The speakers, you want smooth and well-controller off-axis.

19%: Room placement and treatment

1%: Gear; the only way an amp or whatever can affect imaging is will poor channel balance and channel separation (crosstalk); if you paid over $300 for a stereo power amp and it has poor crosstalk (~30dB), it’s junk. Even the $350 Crown 1502 amp (meant for PA, but some use for subs and speakers) has >55dB or separation at all frequencies, that’s lower than the hearing threshold for THD.