Complex sentence: As part of the artistic aims of the "ADMV", annual "Tonkünstler-Versammlungen" at differnet locations were to be arranged, with performances of important, rarely heard, and especially new musical works of all kinds.
Split into simpler sentences: As part of the artistic aims of the "ADMV", annual "Tonkünstler-Versammlungen" at changing places should be arranged. There should be performances of important, rarely heard, especially new musical works of all kinds.