Over the course of a five-decade career, Sir András Schiff has regularly presented cyclical performances of the works of those composers who are particularly important to him. His latest concert series at the Pierre Boulez Saal puts a different spin on this idea: in six concerts over the turn of the year, Schiff dedicates each program to one of the musical masters who have most profoundly shaped his artistic outlook, culminating in Bach’s unfinished The Art of the Fugue.