Hi Having been a Yamaha multi keyboard specialist,music school teacher and principal, and Hi Tec tutor I have never found the OS on any of the products easy because all the products in the 80's were made by different divisions which meant the products were not MIDI compatible,which is very difficult to explain to a customer who bought items from the ONE company yet they would not work together!!!! ie:- a Yamaha HS8 and prs70 keyboard Hi Tec sound modules,just 1 midi channel wow, Technics at the time would iteract keyboard/organ /piano pr series.That was part of the reason I became a Technics retail dealer. The public were starting to expect inter unit compatibility and the same OS for each type of unit not one for organ(electone),portable keyboard/clavinova, Hi Tec/DX-SY sound modules type products
etc. Now a very happy owner of a KH 7000
Regards John.