How to setup CC-ing

[Littleburst]

I get what you describe here but this is what it does for me.

I target a mob, press alt 1, nothing happens. I switch to the char and press alt 1, then it works.. Seems like the alt 1 press isn't send to the slave. When I've done that for multiple chars I want to shift X for the cast (poly/root/hex..), it isn't send to the others, when I set repeater 'on' and press shift X, then it works.. But that's not how I want it to work obviously

Did you add the binds to the ISboxer keymaps? Seems like that's the problem. You can also active broadcast all for a second to test it, then add the keymap later on.