Yes, remember that control room is for monitoring AFTER the main out, so is specifically used in a hardware multi-output setup so that you can output the same audio to different speakers with different calibrations, or different cue mix to different musicians etc. It’s very much a physical output aid.
But you’re doing everything in the box, so you don’t need to use such features. You can use busses and ‘virtual’ audio cables within Cubase if you want to route out audio from application to another.
And as a headphone user you may like to place ‘virtual room’ plugins to the control room to help mix with a simulated room setup via headphones, or apply EQ for monitoring purposes. That would be the main use for Control Room.
Basically anything applied to control room doesn’t affect your project, or is included with the mixdown.
Anyway, i digress… i’m still just not clear on the issues you’re having haha :).
If you change the volume of the vocal mix in Cubase (By that i mean the vocal fader within Cubase’s own mixer), it should do what you want. Also, you mentioned a ‘doubling’ affect at the start of our conversation, is that still occuring?