Smooth treble

You can have the best of both world`s, "..natural sounding" AND "..super transparent treble", via ribbon tweeters, Magnapan, Quads, and some (expensive) high end box speakers.

the bright, brilliant and super transparent treble many people want when they are making the transition from "mid fi" to "high end" audio

Agreed. However, I would replace "super transparent" with "super prominent".

Smooth does, of course, mean there is no jagged & annoying response in the region of 4-9kHz, usually mistaken for "transparency"... as in, "wow, a veil lifted and my jaw fell through the floorboards". I've heard that said of a sibilant set up. Regards

Smooth means not course or irritating during extended listens.

"How can one get this smooth and refined high frequencies without severe treble roll off? "

For me it was a progression of things , of course the recording is the number one component .

I started by ditching metal tweeters in favor of soft dome or organic tweeters . As mentioned above ribbons will fall into this catagory as well .

I then ditched my SS CDP for a tube unit .

Then I ditched my SS amplification for tubed .

And finally finding a tubed int. amp with good top end extension .

It was a process of changes that taught me things along the way . This is not the only way but it is the way that works for me . And other things were accomplished along the way that increased my listening enjoyment .

While I believe that the smooth treble aspect can be accomplished with metal tweeters and SS components , it may come at a greater cost and may or may not give you the desired overall sound that pleases you .
For me it did not .

Good luck .