Mainstage: how to split a MIDI keyboard and route to separate plugin per split zone?

Ok, I found out myself; took several days; the problem was that the signal flow is totally unintuitive and there is no diagram for it; so it took a while until I realized that each physical keyboard has first to be modeled by a visual representation on the layout screen; then you can create instrument strips which can be associated with the visual representations of the keyboard, and in the inspector pane the key range of the strip can be set so that implicitly split zones are formed.

And now for the mapping; there is in input pitch mapping, but it is implemented as a curve which is impractical for the present use case; I found that for the strip reprsenting the drums pluging a midi effect has to be set; the only applicable midi effect for the use case is the "Scripter MIDI Plugin"; there is a pre-defined script for drum mapping, but I decided to write my own one which is work in progress; not sure yet whether the Java Script processing per MIDI event is fast enough; will see.