Complex sentence: Furniture music appeared as the launchpad for minimalist/experimental/avant-garde music since it was the first instance of music being played or produced out of context: not as a centerpiece but as a cerebral backdrop.
Split into simpler sentences: Furniture music appeared as the launchpad for minimalist/experimental/avant-garde musics since it was the first instance of music being played or produced out of context. Music not as a centerpiece but as a cerebral backdrop.