The most important factor in soundstage imaging

@whart :    "Even with a good system, well set up in a room, a lackluster recording, mastering, etc. will sound very disappointing"

Agreed and wonder why this isn't always mentioned first. As I understand it, to have a good sound stage there has to be intention on the part of the engineers/producers. If they don't make that effort and know what they are doing then sound stage will be lacking or if not lacking, a matter of circumstance. And it seems like tweaking a system using a poor recording would be frustrating and counterproductive.

So it seems like the first point of advice would be to start with a good recording. I've got The Who's first album. It is in mono. It is not my sound stage reference recording.

akg_ca, +1 and Mijostyn +1, then- there's TUBES!

Whenever imaging or soundstage are mentioned, I like to remind people about these resources: The following provide tests, with which one may determine whether their system actually images, or reproduces a soundstage, as recorded. ie: On the Chesky sampler/test CD; David explains in detail, his position on the stage and distance from the mics, as he strikes a tambourine(Depth Test). The LEDR test tells what to expect, if your system performs well, before each segment. The Chesky CD contains a number of tests, in addition to the LEDR. (https://www.audiocheck.net/audiotests_ledr.php) and (https://www.amazon.com/Chesky-Records-Sampler-Audiophile-Compact/dp/B000003GF3) The shape of your ears’ pinnae is also a variable, regarding your ability to perceive images/locate sounds. A Stereophile article, that explains the LEDR test: http://www.stereophile.com/features/772/

@n80- I think part of it is the context of the board, which is gear centric. No disrespect intended, since many of the contributors here are well established,knowledgeable, etc.
I was stuck in "audiophile land" for decades, listening to what I now consider to be pablum- sonic wonders with the musical substance of cotton candy. Jumping into record collector world, it’s the opposite- pressings treasured for their rarity, not necessarily their sonics (or even the music).
To me, it’s fun to straddle both worlds and between them, find music i enjoy that sounds good. I geeked enough to build a good system or two over the years, and hung out with the record collectors enough to learn about the deadwax, pressing plants, mastering engineers and labels. But ultimately, it comes down to how it sounds. And that’s where I think the audiophiles and record people sometimes overlap. (The music itself- the performances, the compositions, the playing, is yet another whole layer of stuff- perhaps the most important).  
I’m in a mood, so please don’t read this as snark. It’s meant more as self-criticism, if anything. I can always learn something about both worlds--that’s why I hang out here, on the gear side (and occasionally, somebody mentions an interesting band or album). But, this is a gear centric place, record collecting is about the rarity or obscurity and there’s a whole other world that is about the music itself. It’s a happy thing when all those different strands combine to make magic.