The Tate recently posted streaming audio for their collection of the cassette series Audio Arts. Originally started in 1973 by sculptor Bill Furlough, the series continued sporadically until around 2006. Each issue was a multi-volume set, featuring mostly interviews with artists of various disciplines, assorted sound works, lectures and readings of artists' texts, and the like.
Among the artists contributing or conversing: John Cage, Buckminster Fuller, Dan Graham, Richard Hamilton, Carl Andre, Joseph Beuys, John Latham, Mario Merz, Dieter Roth, Vito Acconci, John Berger, Les Levine, Daniel Buren, and many many others. The primary editions of the series can be found here, will a separate archive for the numerous supplementary editions here.
The prevalence of interviews and blahblah might be of limited interest to many; but if its actual soundworks you want, Ubuweb has (in case you missed it) almost all of the Harvestworks's Tellus Audio Cassette Magazine series archived for listening and download purposes.