Have you had other people over to listen to see if they hear the same things you do from the various component changes? This is an area I’m interested in. It’s not clear why a change in a DAC or amplifier would have a perceptual effect on the soundstage, and it’s not clear that it works the same for everybody in the same situation. Our ability to detect the direction and distance of sound seems to be somewhat of a contextual expectation effect. So a subtle tonal shift can be interpreted as just bad tone, or as good tone coming from a different direction. I’ve had this effect flip on me right in the middle of listening to something. A loud noise from nearby can re-set my aural perspective and suddenly the stereo sound field collapses AND the tone sounds funny.
One thing that’s undeniable about 2 channel or even multichannel audio is that it is filled with crosstalk anomalies that you don’t experience from real instruments playing in different positions in space. In the real case, there’s always a consistent way the sound from each instrument hits your head from that direction. So as you turn your head or move around the room, they stay where they are, and everything is easy for your ears and brain to interpret and make sense of. When you start dealing with phantom images, sounds that are supposed to seem like they’re coming from a different direction than they actually are, there are inevitably inconsistencies that the brain/ear system has to interpret. There’s no guarantee that we’re all going to interpret them in a way that sounds good to us. But there may be ways to make it a lot more stable and reliable so that we’ll get the experience we expect and want practically all the time.
I’ve gone to up-mixing 2 channel audio to 3 speakers myself, using a simple crosstalk reduction scheme with all 3 speakers fairly close together. This started off as an experiment but it’s now been going for close to a year now and I’m remaining extremely satisfied with how easily it lets the speakers disappear to create a nice wide soundstage with depth, stability, and perceptually nice tone for me.
I’m finding that being perceptually properly oriented to your system is at least as important as the quality of the components and the listening room acoustics. Quality components and good room acoustics I think do help with maintaining proper orientation in terms of the sound stage. I think some listening arrangements are easier to aurally adapt to and stay oriented to, so the requirement for equipment quality goes down in terms of maintaining a sound stage, although you still can hear improvements in other areas such as dynamics, tonal purity, etc. from using better components.