Thank you Layzer! I did not use your list, but you pointed me in the right direction. The actual SYSEX formula that works for negatives values in the Korg Z1 is
lt (modulatorValue, 0, 16383 - (abs(modulatorValue)), modulatorValue)
Somehow I did not understand properly how the large numbers are translated to MSB and LSB… I would be grateful if you could explain a bit how you obtained the 16383 value.
Regards and thanx again! Now i am flying with the panel.