I asked Kurt about his lost archives, and he gave me this link for reference. I hadn't had the chance to read his long post 'The Big Picture'. The post on faith at the top is also excellent.
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Using that post title got me wondering about the source of its use on Brian Eno's Before and After Science. I found it:

Kurt Schwitters "Ursonate" ("sonata in prime sounds") is, along with Satie's "Vexations" and Messiaen's "Modes de Valeurs et d'Intensités", one of those mythic pieces that most people have heard about but never actually heard. Schwitters-better known as a major painter, sculptor and key figure in the post-Dada movement- recorded his epic forty-two minute sound poem in 1923, but to the best of my knowledge that version is not available on disc (though bits of it were swiped by Brian Eno for use on the track "Kurt's Rejoinder" from his 1977 album "Before and After Science")...