This discussion includes enough over analyzing that I am compelled to make an attempt to contribute.
I think of objective as being certain and without question.
Example: Speaker A has more drivers than Speaker B
I think of subjective as being open to bias.
Example: I prefer the sound of Speaker A when compared to Speaker B.
All listening tests are affected by personal preference so are therefore subjective. If A/B testing were to show that the listener can reliably identify a difference in the sound when a change is made to the system, it demonstrates that there is an audible difference. If another listener cannot reliably identify a difference in the same setting, it most likely demonstrates that the listener is unable to perceive the change.
Some people have the ability to taste or smell things that the majority of people simply cannot and some of these people are literally paid to taste and smell things. It stands to reason that some people are also able to hear things that the majority of people simply cannot. It's also reasonable that some of these people would enjoy music and become members of a forum such as this.
If a person that can hear things that the majority of people simply cannot also has an amazing audio system, it is very reasonable that they will be able to describe things that the majority will simply never be able to experience. Horton Hears a Who comes to mind. I do believe that some audiophiles suffer from expectation bias and placebo and have convinced themselves that they are hearing more than they really are.