Hi angus12345,
Thank you for your message.
The mixer faders can be used to change the levels of the internal instruments, or other 3rd party apps connected via Audio Unit or similar.
Given the ATV AD5 supports this, MIDI CC might be an option to change the volumes in your drum module from within Cubasis.
Please learn more in our dedicated How to Use Automation and MIDI CC’s in Cubasis tutorial.
Hope that helps!
Best wishes,
Lars