I'm a big fan of Robert Ashley's Perfect Lives and The Wolfman, some of his other stuff I can take or leave, but on the whole I enjoy his work a lot. Alvin Lucier's I Am Sitting in a Room is probably the best process piece I've ever ever heard, not such a fan of Music on a Long Thin Wire, which is the only other piece of his that I've heard. My experience with Gordon Mumma and David Behrman is either close to or actually zero, every time I see their names I resolve to check them out but for some reason I never do — recommendations welcome.
At the very least, add to your list:
Robert Ashley:
Automatic Writing,
AtalantaAlvin Lucier:
Music For Piano With Magnetic Strings,
Music For Solo PerformerGordon Mumma:
HornpipeDavid Behrman:
On The Other OceanI know that some guy is specifically a huge fan of Ashley's
In Sara, Mencken, Christ And Beethoven There Were Men And Women. I'm getting there.
My catalogue of Alvin Lucier is way more expansive, but if you don't care for his work with the pure wave oscillator, that narrows down the list a good bit. Maybe you just think the waves need to be accompanied, in which case perhaps you should try
Crossings or
Small Waves, for instance. Otherwise, go for earlier works.
Vespers,
Memory Space, etc.
Really that whole Mumma Tzadik disc is incredible. I'm currently exploring him more via New World / Lovely releases.
My Behrman knowledge is a bit pathetic too, tbh.