So I compared all uae generated 68k library and modeinfo structs with the fs-uae structs and (for me) everything looked ok.
So after quite some debugging, I decided to annoy Toni with my problem .. and he pointed me to a zero clockrate in my modeinfo structure .. which really caused the above mentioned crash.
Problem was, that I added
int default_freq = 0;
as a stub in aros.cpp and while merging newer WinUAE sources later obviously changed picasso96_win.cpp as a quick hack to make it compile to
int default_freq = 50;
which finally lead to a zero PixelClock..
Big thanks to Toni for pointing me in the right direction!
So now I can see all Picasso96 modes: