The Pittsburgh Symphony has has financial difficulties in recent years. It’s waiting for a new music director, and it’s about to negotiate on a difficult new contract with its musicians. Still, ticket sales that are their best since 1998-99, and last fall got a $29.5 million pledge from the Richard Simmons family, the fifth-largest gift to an American orchestra. “The truth is, the 2007-08 season that starts this month could go a long way toward determining whether the organization can maintain the stride of a first-rate orchestra or fall behind.”