6. John Adams, Harmonium (1980 composed, classical, modern era) C
This is a bunch of people singing, opera/choir style, and a bunch of musical instruments, called an orchestra. It is apparently based on poetry of John Donne and Emily Dickinson, but that should become quickly obvious after you hear the unintelligible (latin? idk) singing of the singers...or not.
Have you ever turned off all the lights, laid down, and put two speakers on either side of your head, and just allowed the sound to fill you? I used to do that with Dark Side of the Moon. Later with The Downward Spiral. Harmonium might be a good fit for that method.
Harmonium has a quality that I don't find too often in modern-era classical music--strong progression tied to traditional chord changes meant to evoke powerful emotion. The second half of Harmonium is amazing.