A number of ways to do this. Here’s my approach.
For a simple solution, I would have a different CC for each rack volume, but then re-map the incoming CCs to point them at the racks I need to control. You can change this mapping on a State-by-State basis.
But…
Way back I created an MCU-compatible ‘mixer’ rack, and I route my instrument racks there, such that I can have any instrument(s) on any input of my ‘mixer’ and control the mixer faders. I could have my pad instruments on Ch1, and my leads on Ch2, for example. Faders use MCU standards, which are channelised pitchbend messages, but mapping a CC to channel/pitchbend is simple.
If you want to try it, the latest version is at the bottom of this thread: Mixer Rack
Ignore the MDP part - if you want that I’m keeping an updated version in MDPs Q&A pages.