I don't have a Keylab MKII. At least not yet. I can only give you suggestions.
When you write, "There is only global settings for passing thru incomming messages," you mean settings to control whether (for example) incoming CV is sent out again as midi, correct?
This is how the manual describe the global possibilities for this:
MIDI In to USB On/Off - Choose whether to pass incoming MIDI data to USB host
USB In to MIDI Out On/Off - Choose whether to pass USB host data to MIDI Output
I don't think Keylab MKII recieve CV messages. Why should it?
When you ask, "Can't you assign buttons to mute instruments or similar?" Do you mean buttons on the Keylab? That's a good idea. I could mute midi by switching to a channel I'm not using. And I could mute Analog lab by pulling down the master volume slider. But it won't work for CV.
I mean any control on the keylab, that work best for a certain task. For mute i think a button or pad is great. For volume a slider or knob and so on. Anything that work for you with any parameter will do.
I would assume your CV possibilities is only restricted by what's possible to control on a synth, and by the fact you only have 2 CV mods. As far as i can tell Keylab MKII can use any control for the CV mods, - and you can even send Midi CC messages through the CV mods, if the Mod CV source is set to Midi.
SO why should'nt it work for CV?
Have you read the manuals and look in your Midi Control Center (MCC)? I suggest you do.
And i suggest you try it out.
And i mentioned a mixer. That can be a good tool. How do you mix your audio outputs from all your soundsources?