Complex sentence: Max Kalbeck reported that Brahms wrote and then destroyed more than 20 quartets before submitting these two for publication, and that he insisted on hearing a secret performance of the first drafts, after which he made heavy revisions.
Split into simpler sentences: Max Kalbeck reported that Brahms wrote and then destroyed more than 20 quartets before submitting these two for publication. Brahms also insisted on hearing a secret performance of the first drafts, after which he made heavy revisions.