Sorry, but I don’t get the issue.
You’ve opened Halion Sonic SE and activated Output 2.
Halion has 16 Audio Outputs that you can use as Audio Channels
in Cubase. You can automate almost each parameter of an Audio Channel
in Cubase. The line next to the audio channel shows the volume automation
by default. Activate “Read” and you can use the pencil tool to draw an automation
into it or activate “Write” to use the controller (in case of volume it’s the fader)
to record an automation.