On the UR816C you can only choose “DAW direct” 1 till 8 for the outputs.
With an external ADAT interface connected you have 16 outputs but it is not possible to connect them to 16 Cubase channels, only 8 DAW directs are available.
I still don’t understand why this is not possible.
This is a great lost of use with this unit. My main use is for connecting external hardware.