@jojo3110 : are you sure your MIDI interface is handling system-exclusive messages correctly at all ? A lot of (cheaper) USB MIDI interfaces make a mess out of system-exclusive messages. Maybe you could test with NRPN (=regular MIDI control messages) instead ?
example (KPA's MIDI channel set to '1' or 'omni') : send 4 control messages as follows:
AMP on = B0 63 0A B0 62 02 B0 06 00 B0 26 01
explanation:
B0 63 0A = NRPN parameter number MSB (set to 0x0A -> address page = 'Amplifier')
B0 62 02 = NRPN parameter number LSB (set to 0x02 -> parameter = 'On/Off')
B0 06 00 = NRPN parameter value MSB (set to 0x00)
B0 26 01 = NRPN parameter value LSB (set to 0x01 -> switch 'on')
likewise:
AMP off = B0 63 0A B0 62 02 B0 06 00 B0 26 00
note: in 'running status' mode the same messages can be sent as:
AMP on = B0 63 0A 62 02 06 00 26 01
AMP off = B0 63 0A 62 02 06 00 26 00