@Ohki

Thanks for the advise.
JCM's are basically multiple morphs controlled by one bone movement, right?
If I remember correctly, it is done in this dialog who one can teach the bone to control the movement of other bones and morph targets as well.
You select the bone and start recording what other parts of the skeleton should move accordingly, right?
The hint with the adding of groups without re-grouping is also very useful, it did not came to my mind, like at all.
That is much to cover, I will keep posting my results as soon as I make progress.
This is getting really interesting.