Levin reacts to this text as follows:
Such practice, he now argues, enlists the element of chance (which is unavoidable in all performance) in the service of reason, and exposes the falsity of the ideology of inspiration that is already incompatible with the iterated structure of traditional rehearsals.One cannot read passages invoking “the element of chance” (or, for that matter “the falsity of the ideology of inspiration”) without thinking of Cage. However, there is still the question of whether Adorno himself was thinking about Cage when he wrote this sentence. We may never know for sure. On Everything2 we can find a post by the user Oisin that includes the statement:
So Adorno included John Cage among his composers to be championed, for although his work is not dodecaphonic it is "atonal" in the sense that Adorno uses the word.However, Adorno’s interest in montage is not necessarily related to his advocacy of atonality, nor does Oisin state explicitly whether Adorno actually knew who Cage was or had hear any of this compositions.
These questions may be resolved somewhat more satisfactorily by a sentence in Adorno’s “Art and the Arts” essay from 1967, which is included in the Stanford University Press anthology, Can One Live after Auschwitz?: A Philosophical Reader. The sentence in question is the following:
What set out to spiritualize the material of art ends up in the naked material as if in a mere existent, just as was explicitly called for by a number of schools—in music, by John Cage, for example.In other words Adorno knew enough about Cage to know that he believed that any sound could be treated validly as “material of art’ (although we have no idea from this sentence whether Adorno actually listened to any of the ways in which Cage put this theory into practice!