Complex sentence: Planyavsky has recorded all the organ works of composers such as Johannes Brahms and Felix Mendelssohn, and has conducted not only the great works of sacred music but neglected organ concertos such as those by Alfredo Casella and Aaron Copland.
Split into simpler sentences: Planyavsky has recorded all the organ works of composers such as Johannes Brahms and Felix Mendelssohn. As a conductor, not only performed the great works of sacred music, but neglected organ concertos such as those by Alfredo Casella and Aaron Copland.