The Pittsburgh Symphony Orchestra, in the early stages of its search to replace departed music director Mariss Jansons, will fill the leadership void with a triumvirate of conductors in supporting roles. Sir Andrew Davis will take the title of Artistic Advisor, and will program most of the orchestra’s concerts. Yan Pascal Tortelier will become principal guest conductor. And Marek Janowski will be a guest conductor with a specially endowed chair. The arrangement is already being compared with the innovative (and controversial) leadership model adopted last year by the Saint Paul Chamber Orchestra.