Thank you all for your help and insights.
I realize now that it is time to change my workflow and get back to working with my daw, because it is probably much easier than trying to perform midi-miracles within BiaB.

@DeaconBlues
It is the full version of FM8 (I bought Ultimate 11), so it must be something else which is causing my problems. And thanks!
@Jim & Noel
As you suggest, I will try with some other synths and see if they work better with BiaB, because I would really like to hear better sounds when browsing the midi styles.
Will