Even as the Chicago Symphony prepares to usher in a new era with the departure of music director Daniel Barenboim, one familiar face at Orchestra Hall won’t be going anywhere. Pierre Boulez, the onetime enfant terrible of contemporary music, has made a home for himself in Chicago as the CSO’s principal guest conductor, and some would argue that his effect on the orchestra has been more profound than even the music director’s. “His presence has enlivened the contemporary music scene throughout the city. Some listeners who hear his lucid, highly honed performances of new music with the CSO have been tempted to seek it out elsewhere.”