Tube sound is not about warmth. It's about correct presentation.

But what is it in the sound that gives this?   It is not just more harmonics as that is synthesized in modern DACs and it is no where near the same. It is not linear distortion as tubes can be as flat as anything. ( And it is easy to turn down the treble ).  Is it the better dynamic linearity?  Is it a clue that a 12W tube amplifier can sound as "big" as a 100W bi-polar?  Less IMD? Difference in how they behave at clipping vs SS? Higher noise floor that masks nasties?  Or a noise floor that is more constant and not pumping?

I think, first of all, with SS something is missing. It's a negative coloration. Then there is always this metallic element to their sound. That's positive coloration.

What does 'correct presentation' mean? 

There is timbre presentation, there is all spatial aspects of the presentation , there is the general immersiveness impression ...

Today  nothing of that is reserved to tube amplification or to S.S. amplification...

Each tubes amplifier and each S.S. amplifier is a specific case... Now add to that class D ... And any other variation ...Between integrated or amp and pre-amp...

As larsman just said :

What does 'correct presentation' mean? 

Prejudices are not knowledge...

Regarding perceived tube warmth, isn’t this even order harmonics at play?