Complex sentence: In 2006, the 250th anniversary year of Mozart's birth, the Theater an der Wien presented a series of major Mozart operas and it has since become a full-time venue for opera and other forms of classical music under the direction of Roland Geyer.
Split into simpler sentences: In 2006, the 250th anniversary year of Mozart's birth, the Theater an der Wien presented a series of major Mozart operas. This initiated its conversion to a full-time venue for opera and other forms of classical music under the direction of Roland Geyer.