What contributes most to a change in how an amplifier sounds?

To be honest I can't hear much difference when I swap between my 3 power amps. My 600 watter definitely has more oomph. Maybe its just nostalgia but I do like my old Phase Linear 400, however my ears are now, low-fi.

I have to say this has been one of the most entertaining topics I’ve heard in a long time!

I inserted ‘real life speaker load’ into Google search and got this fascinating AI explanation. I was intrigued by this term that I read above. The AI info is less than helpful and doesn't really answer things very well.  

AI Overview

Learn more

A real-life speaker load is more complex than a resistive load, which is what amplifiers are usually measured against. Here are some things to consider about speaker loads:

• Impedance

  A speaker’s impedance varies depending on the frequency it’s playing. The stated impedance is usually measured at 400 Hz, but a speaker’s impedance can vary widely across the frequency range. For example, a speaker’s impedance can be up to five times its rated impedance at its resonant peak.

• Acoustic load

  The acoustic load a speaker experiences depends on how it’s coupled to the surrounding structures and cabinet. For example, a speaker placed in a horn will have a higher acoustic impedance than a speaker in free space.

• Power handling

  Using an amplifier that’s too small and driving it to distortion levels can damage a speaker.

• Matching speakers to amplifier

  It’s important to match the power output of your amplifier to your speakers. If your speakers are underpowered, the sound will be thin and hollow. If your speakers are overpowered, they could distort and become damaged over time.

• Calculating speaker load

  When speakers are connected in series, you can add the nominal impedance of each speaker together to calculate the total impedance.

All things equal isn’t 240 volts superior to 120? I always wondered how much detail a 120 volt system is missing.

https://www.stereophile.com/reference/707heavy/index.html