why do expensive amplifiers produce a better soundstage

I experienced a "walk-in soundstage" when i owned my first dedicated acoustic room which was tuned by 100 Helmholtz resonators...

i had an excellent soundstage but not a "walk-in soundstage"  in my actual acoustic corner in more nearfield listening conditions...

for me it is the acoustical mechanical control of my system/room that was the key not the price of my gear... (my system cost was around 1000 bucks) 

@faustuss  My experience in soundstage was previously articulated here:
https://forum.audiogon.com/discussions/walk-in-soundstage?highlight=walk-in%2Bsoundstage

Since then, I have upgraded several front-end components: the streamer to Volumio Rivo Plus ($1,650), the I²S cable to Veritas Optimus, and the XLR interconnect to Veritas Magnus. As a result, the soundstage has become even more immersive in all dimensions. Compared to before—when the soundstage was wide but low and relatively flat with the budgetary streamer/dac—the presentation today is distinctly three-dimensional.  Notably, I have not changed my amplifier (Parasound A23, $650 used) or speakers (Wharfedale Lintons, $1,500 new). I also reintroduced the Schiit Saga 2 ($280) into the chain. The DAC currently used is the Harmony Micro DAC ($950).

I list prices intentionally to highlight that the amplifier and preamp are the least expensive components in the system. Yet, they have proven fully capable of preserving and restoring the soundstage information already present in the recordings when paired with the right front-end components. In contrast, my previous digital sources—streamers and DACs—effectively collapsed depth and masked layering, resulting in poor separation and diminished spatial cues.

To be clear, I am not suggesting that the amplifier at the back end of the chain does not matter for soundstage presentation. Everything matters—the entire chain, setup, and room—when it comes to preserving spatial information embedded in recordings. However, many affordable amplifiers today already offer competent specifications (sustainable current delivery, damping factor, slew rate, and low noise/distortion) that are important for accurate soundstage reproduction.

In my experience, this means that amplification has increasingly become a necessary condition rather than a sufficient one, whereas the front-end components—particularly digital sources—have a disproportionate impact on whether spatial cues such as depth, layering, and image separation survive the signal path at all. At least in my system, and based on my listening, the primary bottleneck was clearly in the digital front end, not the amplifier.

I agree with amplifier design first. Then power supply and component quality.

@emergingsoul 

Thank you. I am indeed fortunate.

@lanx0003 

"...streamers and DACs—effectively collapsed depth and masked layering, resulting in poor separation and diminished spatial cues."

"At least in my system, and based on my listening, the primary bottleneck was clearly in the digital front end, not the amplifier."

This was our biggest complaint with digital early on, it was the DACs not the recording or the format.

@fiesta75 

"I agree with amplifier design first. Then power supply and component quality."

What's coming out of the speakers is the power supply being modulated by the source (music).

Musicality and soundstage.

I think it’s a question of balance, gleaming the best from all of your systems component parts. Not to be forgotten is the room, it is also becomes a musical instrument. A rooms musical/acoustic footprint finally defines the soundstage.

As an example, music played with speakers placed 10 yards apart will still produce a musical black hole, even with $10,000 interconnects.