What stereo equipment do respected musicians listen to?

Jimi Paige has been photographed using a Luxman preamp with McIntosh amp.

McCartney has two Garrard turntables in his listening room per photos. 

Marvin Gaye was photographed with Mac amp, Thorens turntable, and a Teac reel-to-reel. 

Magic Johnson was a DJ at Michigan State.  When he made money in the NBA he had a pretty sweet system, but I don't recall what the gear was at this time. 

Jay Z: Nagra and Devore O96

My experience is that self-designated audiophiles are extremely rare in the general population.  I would expect the same amongst professional musicians.  Classical or other acoustic music might on the whole be a bit more picky about accurate reproduction of the instruments with which they are most familiar.

The OP asked: "What does Wynton Marsalis listen to?".

For speakers the answer is Tetra.

Full disclosure, for years I was the only ATC dealer in California.

Now, retired, I consult in marketing for Tetra Speakers ( dot com).

It is quite true that many top artists, major studios and the world's greatest concert halls use ATC powered speakers. Artists mentioned and many more. 

In studios and concert halls, accurate presentation of the sound recorded and amplified is vital. +1 "extremely dynamic, supremely accurate". 

However, even though many artists want to experience music in their homes as they have in the studio, that sound is not necessarily what is desired in the home.

+1 "professional studio monitors and that ilk have a different set of design parameters entirely. Near field and hear all the details."

I first became aware of Tetra speakers when I fortunately got a pair of their mid line 506 speakers. I heard from those speakers what I have never heard from ATC or any speaker in 50 years: shockingly realistic music. And when I got a pair of Tetra's entry level speakers, the 120Us, they sounded as real as the 506s just on a smaller scale. 

And when I went to their website I saw the rave comments of many of the world's greatest artists. They all are dedicated and proud Tetra owners. From Herbie Hancock to Ron Carter to Dave Holland to Keith Richards, etc., etc.. Herbie has 6 pair and Keith takes a pair on tour.

Some may say, what do artists know of what is possible in High End Audio?

Tetra artists say that their Tetras sound like the hear themselves on stage.

I say, who would know better?

"They probably listen much more to the notes than the sound of the instruments."

Speaking for myself, I am very aware of every Note and Sound that is coming from Me.  As well as the notes and sounds coming from others in the band or orchestra.