I have difficulty in the programming of program change. In options there are 20 groups and 10 sound. EXAMPLE: If the first group check a program Group 1 (Piano) and sound 1 (Grand Piano) is fine for all the group 1 and 10 sound. If you want to program group 2 (El.Piano) and its 10 sound does not have the possibility of programming since the 10 sound are already engaged by the first group.