I believe when the X-4 or other controller calls for a sound that is in a bank higher than the 128 gm sounds in the SD2, it cannot access them (unless you program the alternate control change commands for the higher banks) and thus reverts to the bottom of the list- the piano sounds. I have this problem with the SD2 and my Orla KX-10 keyboard. The Orla's programming is not sophisticated enough to select control change commands other than "0" which again will access only the first 128 sounds in the SD2. So sound # 129 from the orla will call up sound #1 from the Ketron. I can however do so with the Excelsior Midivox controller I had on one accordion and with my Totter midi as well.