Solid state amplifiers and sound stage, especially front to back "depth"

No doubt different amps will have different transfer functions that could result in the parts of the signal that determine imaging and soundstage, many of which are very low level, being reproduced differently.
A linear transfer function is generally what is desired on paper but it’s likely the case that no two amps have exactly the same transfer function be it linear or not so linear. Transfer functions that emphasize the lower level parts of the signal that determine soundstage and imaging could even be artificially emphasized in a way that increases soundstage and imaging even if that is less linear. I would expect that amps that soft clip where dynamic range is compressed (many tube amps) and that also feature very low noise floors could excel in soundstage and imaging. Even if an artificial artifact of the amps non linear transfer function when soft clipping it might be regarded as a desirable effect.

In that context, my Bel Canto ref1000m amps also do soft clip but effectively never do in that they are 500 w/ch into 8 ohm doubling into 4 ohm. However, they are also absolutely dead quiet so together the effortless dynamics and low noise floor combine for quite exceptional soundstage and imaging (also dynamics) I would say with a very linear transfer function. Nothing artificial there.

Regarding an amp or any other electronic gear upstream’s relative ability to do imaging, it’s generally about achieving low distortion and detail retrieval. That is needed to best deliver the spatial cues that enable imaging captured in a recording completely. Then how the recording is made is the other in big factor.
Then of course the speakers setup and room acoustics determine exactly how those cues are rendered and imaging and soundstage actually produced.
The best soundstage depth Ive ever heard by a huge margin was an all mbl system with SS amplification set up in a highly customized showroom. With master recording R2R as a source you could easily identify exact location of individual orchestra instruments both front to back and side to side in a large tapered rectangular area. That was at now defunct United Home Audio in Annapolis Junction, MD several years back. Nothing else I’ve ever heard comes close on regards to precise 3-d soundstage and imaging depth. Totally holographic. Same setup by same vendor was just OK at local shows in more conventional and less optimized room setups.

In my system, holographic soundstage and imaging took a big leap forward when I introduced the Bel Canto ref1000m Class D amps to my Ohm Walsh speakers. It was totally disorienting at first until my ears latched on to what was happening. Night and day from prior Class A Musical Fidelity SS amp.