When it comes to the Faustus passage, Mann’s narrator could not analyze the string quartet in more detail because the piece does not exist. (I think the description was initially sketched by Adorno at Mann’s request? Anyhow the project is experimental in a different way.) The lecture on Beethoven towards the beginning of the novel is closer to what you are trying to do, although it remains impressionistic.

I could imagine taking one of Charles Rosen’s books of music criticism in a sort of Pale Fire direction, with the commentator gradually losing his mind… Or perhaps one could write a musical score in which the performance directions suggest a novel, like the Davidsbündlertänze.

Anyhow it does sound like a very interesting project that likely hasn’t been tried before, a different sort of Gesamtkunstwerk.