JC is right The 2nd movement is in a very constipated sounding Ab min. if the piece is played in Eb (been there, done that). A min (open strings) sounds far more "open" and transparent (been there, done that too). Most, sadly, never have the chance to play the Hummel with an orchestra, and a piano sounds like a piano in every key. Check out Ghitalla's old recording in E (C trumpet) with Pierre Monteux... Best, EC ps: for you Londoners out there, Hummel's manuscript is in the British Museum.