I don't think that a liking for mainstream music has much to do with S or N. I mean, after all, music is music. Mainstream bands are just the ones who got lucky.
I do, however, think that Ns might prefer classical music because of what it tends to do with one's mind -- it's more abstract and requires a bit of personal interpretation. It more forcibly demands attention.
I think S types are more likely to sing along to songs because they're more in tune with what is more direct, but an N will probably be more appreciative of the overtones of music and the more background impressions, such as rhythm, tone, and melody, but not the actual words. They listen to music because it paints imagery in the mind, and requires more abstract, subjective interpretation.
The same thing happens when I'm watching a movie. I tend not to fully concentrate on the story, but more on the aesthetic overtones such as how the scene is put together for purposes of stimulating my own imagination. I have less concern with what's happening directly and I have to watch a movie several times to understand it.
Again, I get this sort of experience with either mainstream or indie films. A film for me is a more operatic experience.
I tend to enjoy mainstream films even more because I am appreciative of big-budget special effects. The subtleties of a digital character and the way an action sequence is done stimulates my mind and makes a film seem more poetic, but again, I have to watch the film more than once to take notice of the story, which is a more direct and concrete aspect of the film.