Days after he debuts in Boston, James Levine will travel back to New York to put his new toy on display at Carnegie Hall, where comparisons between the quality of the BSO and the Met Opera Orchestra are sure to be made by the sharp-tongued Big Apple critics. Over the course of the season, Levine will conduct six Carnegie concerts: three with the Met, and three with Boston. It’s almost as if the same guy is managing the Yankees and the Red Sox, and for classical music fans in the Northeast, it should be an interesting matchup.