OK, the ouput of EZKeys must be routed to the other instrument track... Thanks!
But: It's not the same as in Logic. In Logic all I do within Ezkeys is immediately mapped to the other instrument, so if I browse through the MIDI library from EZkeys, or if I use the chord tool in Ezkeys, all is send to the other instrument, makes it easier to get the results. In a way you can fully exchange the sound engine from Ezkeys thru another plugin. Thats great!