What are we objectivists missing?

@hartf36 The difference could be that I moved an armchair from one corner of my listening room to another, and it completely changed the room acoustics, all else being equal. Does that count?

Yes. The all else being equal being the the objective measurements of the equipment. It is data. It can be banged with a hammer and it will not change.

Then game-on for individual preferences, circumstances (however defined), room arrangements, and exaggeration.

I understand. Indignation.  I use that word with some trepidation as I tip-toe away into a safe zone. .

@jjtucker Well, this did not go in the direction I had intended,

Which intention?

1. My take is that if you can hear a difference, there must be some difference.

...be some difference in what? "Sentence fragment".

2.If a device or cable or whatever measures exactly the same it should sound exactly the same.

No device or cable ever "measure" exactly the same as another. Should they, then they are effectively the same device.

Anyway, cables and {electrical} devices don’t make the sounds that you perhaps are referring to. I digress.

3. So what are your opinions on what those differences might be

See point 1. I dunno, you are telling the story.

4. what are we NOT measuring that would define those differences?

The differences between what and what? Once there is an audible difference, there does exist a test that suggests what is causing that difference. Your assertion that there is something not being measured is one of your own making.

Perhaps if you seek a specific direction, the question must be framed in such a manner that is specific to your enquiry without mistakes of logic. Perhaps refer to a circular reference issue Excel users may occasionally bump up against - it sometimes takes some thought to figure out.