Jean-Louis,
I've had a look at the manual for your keyboard and the Korg should have drums on midi channel 10 by default.
The "Force drums track to midi drums" is only useful if the Drums track contains underlying midi drums in the selected style. From a brief experiment that I just performed, it seems that some of the styles based on Realtracks do not have associated midi drums. It may be that one such style was loaded when you tested the midi drums.
To see if all is working properly, load a 100% midi style. These are styles that do not have
_ or
= or
M_ as the leading character(s) in the the style's name.
Prior to loading such a style, though, you will need to disable the auto-substitute options found under "Prefs | Realtracks" and "Prefs | Realdrums" (see below).


Hope this helps,
Noel