There are many reasons to relish a trip to Powell Symphony Hall in Midtown. There's the beautiful old edifice, a converted movie palace restored to gorgeous splendor, from the gold leaf in the domed ceiling to the Art Deco proscenium and the plush crimson seats and carpet. There's the excited buzz in the lobby, where the monied old codgers whose donations keep the building open rub elbows (if unintentionally) with the college kids who scored $10 rush tickets -- all of them dressed in their finest because a Saturday-night performance here is an event. There's the orchestra, a rich, well-tuned instrument, one of the finest in the U.S. And then there's musical director David Robertson. An accomplished musician who has received armfuls of awards and whose conducting skills are in demand all over the world.