The appointment of Christoph Eschenbach to head the National Symphony Orchestra may have had some unintended consequences. As Anne Midgette wondered in the Post yesterday, has the Eschenbach news deflated the significance of the first concerts led by Iván Fischer (pictured) as the NSO’s Principal Conductor? Fischer may have felt odd seeing Eschenbach’s picture on the marquees outside the Kennedy Center this week — the new Music Director will not actually conduct the orchestra again…