Jazz listening: Is it about the music? Or is it about the sound?

I posted a few months ago that many of my old rock albums sounded pretty poor on my new system - now some I only listen too on an old system I have in my workshop in the garage. I have not heard a really unlistenable Jazz album yet. In fact all The Modern Jazz Quartet albums sound amazing on the new system and have brought me back to listening to more Jazz. I have replaced some of my old rock with 180 gram reissues when available and that has helped.  

assembling a system that can deal with the wide wide range of recording quality of the various forms and sources of music we listen to is a key learned skill in this pursuit

that been said, it is still hard to have cake and eat it too... whereever on the spectrum you choose for your system’s tonality

and oh, yes, to the top line question... it is about the music... the brilliant music... they system is there to convey and hopefully not distract

It's the recording. 
It's the sound of the music.

I have found Jazz to be one of the tougher music genres to reproduce via an audio system. The tone quality of instruments is important with the right balance of smoothness and attack (but without artificial sibilance to the leading edge of notes). But also important is timing and the flow of the music. Systems that lean to much to the side of smoothness (generally tube amps) can sound too slow for jazz. On the other side, solid state amplification that is too focused on resolution can make the tone quality of acoustic instruments sound harsh. My experience is that good equipment for listening to jazz doesn't have to be super expensive, but finding the right blend of equipment to get the right sound personality for your preferences matters. For instance, the quickness of my pretty reasonably priced Monitor Audio Silver 300 speakers seems to allow a lot of leeway for sweeter sounding amplification which will likely be my next purchase (after working on my digital front end.

For me it is all about the music, but how that music is reproduced matters as well. Listening to 'Kind of Blue' right now and it's hitting the spot for me this morning...

I think it depends on the material you're listening to. There are some recordings that have historic significance because of the lineup, the style of jazz, the performance of a particular player or the interplay between band members. Several Miles Davis/John Coltrane recordings come to mind, like the first European tour by the Davis/Coltrane quintet, certain Newport Jazz Festival recordings and, of course, Kind of Blue. In addition to repeated listening, I've read different books and contemporaneous reviews. So, for those recordings, I have much more "encyclopedic" knowledge about the lineup, the venue and the historical significance of the material. 

Then there are those sources where the quality of the recording is superior but there's nothing spectacular about the music itself nor any notable historic significance. I'm much less informed about these albums but I love the way they sound in my room and they allow me to hear deep into my system. Chick Corea's Trilogy albums come to mind. The music itself is stellar, the lineup is superior in jazz terms, and the recording is phenomenal. It doesn't matter to me that they're bot necessarily breaking new ground the way Davis and Coltrane were. I appreciate these albums and listen to them in a different way.

The same can be said for rock music, though. I'm much better informed about historically significant rock albums (Beatles, Yardbirds, Al Kooper) than about other rock music.