Sounds are coming from Yamaha Modx in multi channel midi mode, parts with audi output on usb channel 1&2 and 3&4. The Problem: Cubase 10.5 is not showing these sounds and as consequence not to record. Cubase Audio tracks are switched to monitoring of course.
I use an aggregate Audio device (macos) Modx & Yamaha and i think all mappings are correct.
Did the same setup with Logic and Ableton and everything with the equivalent setup of channel and usb mapping works fine and delivers the sounds from MODX on the dedicated USB channels which i can record.
All Yamaha Steinberg drivers are up to date. This kind of problem i did not had before i installed the Cubase Importer to import Cubasis3 files, which does not work either 
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Something must be weired.