Speakers that can reveal orchestral instruments' positions

First, two speakers cannot image "height". You have two variables, when the sound arrives at each each, and how loud the sound is for each air. There is no way to derive "height" from that, so don’t bother trying .... though you may convince yourself it is there and/or your room acoustics may give an impression based on inconsistent frequency response w.r.t. direction (which is not a good thing).

I get a good laugh when I read people saying they made some minor change and the "soundstage doubled", or some other superlative. As pointed out, most of the soundstage is in the recording, so it comes down to how it is recorded and mixed. Remember, only two variables w.r.t. imaging, when the music gets to each ear, and relative volume.

After that, it is a complex interaction of your speakers and room. If either one is bad, you lose your imaging. On the speaker front, it comes down to the same things always discussed, smooth on-axis frequency response, and smooth decaying off-axis response. If you don’t have smooth on-axis and smooth decaying off axis response, then the volume balance between instruments gets messed up due to frequency response variations. So when you do research, look for products that either publish good on/off axis frequency response and/or where you can find tests on the web. "Trust your ears" it not always the best advice. Speakers will sound much different at home versus in a demo room. You are listening to the room as much as the speakers, and a purpose built demo room can hide problems that you may not be able to avoid at home.

If you aren’t willing to work on room treatments, then forget about good imaging. This comes back to timing. If you have strong reflections, your brain doesn’t know what arrived first and it needs to be able to clearly identify the same signal reaching both ears. This also plays into the importance of smoothly decaying off-axis frequency response. First reflections and strong reflections are all bad. Side walls in front of the speaker, behind the speaker, and often forgotten is behind the listener, but also the floor and the ceiling. You don’t want to eliminate all reflections as then you loose that nice artificial sense of "space".

geoffkait:  "Actually, speakers image height real well unless you have system issues OR you system is not optimized"

No, that is just not the case. I know many want to believe this, but it is physically impossible. It is impossible to encode this information on 2 channels of audio. If the different frequency drivers you are using are spaced far out on your speakers, or have significantly different vertical dispersion, then an artificial illusion of height that bears no resemblance to the original performance, or even what the engineer thinks they are recording is possible, but that will come with it all kinds of other issues. Being an artificial illusion, it is not "imaged", as that would imply a level of accuracy.

iopscrl:  "Not only pinpoint imaging across the space in front of me, but I could hear depth and height !  I could hear fingers moving up and down the neck of a standing bass.  I could hear the relative locations of a trumpet bell, and the mouth of a tenor saxophone. Each occupied distinct space that could be identified as they played in unison. "

That perception of fingers moving up and down the neck of the bass would be your brain filling in information that does not exist. Your brain knows enough about how that bass is played to translate audio clues into a perception of what is happening. Our brains can do a lot to fill in information that we don't have based on prior knowledge. It does work better when we get rid of the other chafe.