Hiring musicians is one of an orchestra music director’s biggest responsibilities. “A music director has to put his stamp on the orchestra.” But James Levine, chosen to be the Boston Symphony’s next music director, wasn’t able to begin the job for three years. In the meantime, what about hiring players? Surprisingly, Levine isn’t part of the process – the players themselves will choose who gets hired. It’s an unusual arrangement – only one other US orchestra chooses players this way – Levine’s Metropolitan Opera Orchestra.