By the time he passed the reins to Roberto Diaz this past spring, Gary Graffman had been the director of the Curtis Institute of Music longer than most of the students there had been alive. This Sunday's tribute concert to Graffman at Verizon Hall reflects the huge impact he has made on the Philadelphia scene. Two of the performers are his best known piano students, Lang Lang and Ignat Solzhenitsyn. Diaz himself, the former principal violist of the Philadelphia Orchestra, will play. Graffman's friend and fellow Curtis piano instructor, Leon Fleisher, will also participate. Like Graffman, Fleisher had a spectacular career as a soloist until he injured his right hand. Philadelphia Orchestra music director Christoph Eschenbach, another great pianist, will take part in a reading of the Schumann Piano Quintet, Adagio movement. That orchestra connection is perhaps the most significant Graffman legacy of all; nearly half of its members have a Curtis diploma adorned with Gary Graffman's signature.