@RickS, thanks for replying, great observations and a great question, which I probably will not adequately answer.
At some point (depending on the recording), there in only so much you can do after the fact. Shy of binaural production any multi-mic recording is going to have a limited ability to reproduce soundstage. So, while I said I could accept stereo's flaws, it is partly because I acknowledge that (for most of the popular music I like), the recording has not captured any meaningful soundstage content.
I think you and I may have different priorities when it comes to soundstage. I'm assuming that, the way we're using the term here, "soundstage" is a broad term that includes "envelopment" as well; please correct me if I'm mistaken.
On the playback end of the chain, my opinion is that, regardless of whether there is a little or a lot of “meaningful soundstage content” on a recording, whatever is there should be reproduced well enough to contribute to enjoyment IF that's something that matters to you.
And I readily concede that soundstage does not matter equally to everyone! I totally respect the paradigm expressed so well by Stereophile reviewer Jason Victor Serinus:
“I'm not so much interested in WHERE the musicians are on the stage as I am in WHY they are on the stage.”
So if you find the soundstage on stereo recordings so unrealistic and/or inherently lacking that it's barely, if at all, worth pursuing, GREAT! That frees you up to put attention and resources into optimizing for attributes which you DO find well worth pursuing.
I might like what I hear at times, but it is at most an artifact of some superimposed effort done in production and by my brain.
For better or for worse, I find it easy to enjoy whatever soundstage is on the recording, be it real or engineered or both. I like being able to hear the apparent locations of voices and instruments, and I like the sensation of being in a larger acoustic space than my playback room. Those attributes help me to “suspend disbelief" and just get lost in the music when I close my eyes. For whatever reason, the artificiality of phantom sound images and listener envelopment is not a distraction to me.
When you take this into account, there are so many variables in producing the content, how can one expect stereo speaker to recreate soundstage information that is either lacking or has been significantly manipulated in the production stage?
Well obviously stereo speakers cannot recreate a soundstage that's not on the recording to begin with, but I don't see why stereo speakers cannot reproduce a soundstage that has been significantly manipulated in the production stage. The room gets a vote too, so imo we're really talking about speaker-room interaction, and not speakers in isolation.
Taking that aspect one step further, when we talk about speaker-room interaction in the context of soundstage (including envelopment), we are talking about the characteristics of the in-room reflection field. And in my opinion THAT is where there may still be a little bit of juice to be squeezed out of two-channel playback.
Anyway, assuming there actually IS worthwhile soundstage information on a recording, let me try to briefly respond to your question of "how can one expect stereo speakers to recreate soundstage information...?". The following will just be my opinion:
At the risk of oversimplifying, in the playback room there are two sets of spatial cues present: The "venue spatial cues" on the recording, and the "small room cues" inherent to the playback room. When the "venue spatial cues" on the recording are perceptually dominant, we have what might be called a "you are there" presentation. When the "small room cues" of the playback room are perceptually dominant, we have what might be called a "they are here" presentation. And there is a continuum of "in-between" spatial perceptions that stretches between these two extremes.
To the extent that we can suppress or disrupt the "small room cues" and/or to the extent that we can facilitate the effective presentation of the "venue spatial cues", we can push the spatial presentation more towards the "you are there" end of the continuum. There are various approaches to doing so; let me know if you want me to get into some specifics.
