I’m using a variety of hardware synths, old and new. Juno-106, Jupiter-X, Peak, Iridium, Virus Ti2 etc. They are all set up as “External Instruments” in Cubase so they are added to the project via an Instrument Track.
If I add a modulator to this track I can select MIDI CC as a destination. When I choose any CC (like cc#1 for modulation) I just get an error “An unknown error has occurred”.
I also tried adding Retrologue as an instrument track and assigning a modulator to a MIDI CC and got the same error.
In this thread it has been confirmed that this is not a supported function: