Jens,
You are probably asking this question in the wrong place.
This forum is about the MIDI standards and how they are supposed to be implemented, not about how an individual manufacturer builds their machines.
Nonetheless, many people here (who are not part of the standards institute) try to answer what they can.
Why don't you try a forum which specialises in Yamaha keyboards such as 'yamahamusicians.com/forum' or '
http://www.psrtutorial.com/forum'?
There you will find many experienced users of the Genos who might be able to help.
On both fora you will have to navigate a bit to find the correct section.
Post a query there, but don't expect instant answers, many are working musicians and have limited time.
JohnG.