A quick check on the KN5000 MIDI.
Initialise the keyboard.
Set the Right 1 volume level to 0.
Select Program Menus, MIDI, Part setting.
Set Part 4 MIDI Channel to 1.
Exit menus.
Ensure that only the Right 1 part is selected and play a few RH notes.
There should be no sound.
Connect a standard MIDI cable from the KN5000 MIDI Out to the KN5000 MIDI In.
Ensure that Part 4 volume level is not muted or set to zero and play a few RH notes.
This time you should hear the Part 4 instrument (Piano?).
If the notes sound correctly then your KN5000 MIDI Out is working and it is probably a matter of settings.
There were a number of upgrades to the KN5000 operating system, but I don't know whether any of these were to correct MIDI problems.
Len