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

If "correct presentation" is clarity and all the good stuff that comes with that, then yes, I agree.  To me the tube "warmth" is just lack of overemphasized, unnatural treble.  

Yes and I am with @knotscott on "correct presentation" or correct distortion. 

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.