If you really want to go out there in minimalism, try Alvin Lucier and Phil Niblock. They are pure tonal minimalists (as opposed to Reich and Glass who are rhythmic minimalists). Also Folke Rabe and some James Tenney might fall in that catagory. You can get all of this on CD, but it is really hard to get on LP.
By the way, I detest Philip Glass, but I love Steve Reich. His "Octet" is one of my all-time favorites.
Maybe also try the more accessible and less annoying John Cage pieces, like the early solo piano stuff. There is a comp called "In a landsacpe" (Stephen Drury performing) which I am fairly confident you would like (based on what you have written).