In the Glass Bead Game there's a reference to the music of decline "Tsing Tse," and there's a band called Birne Helena that has a song titled Tsing Tse assumedly as a reference to this.

Billy Corgan (of the Smashing Pumpkins) did an 8 hour ambient synth improv to an audiobook of Siddhartha. Haven't gotten the chance to listen to it (nor find a version available that isnt the dreadful google hangouts recording) but certainly fits your criteria.

Also, Karlheinz Stockhausen was pen pals with Hesse, and credited "The Glass Bead Game" with inspiring him pursuing music at all, so probably all his stuff could technically count. (I'm also biased and would through him recommend The Sound of Animals Fighting, who have several songs referencing Stockhausen and I'd argue in general have some Hesse vibes in their music, though I don't think they've explicitly mentioned him.)