scmusetup.txt

brew tap thefox/brewery
brew install cmus-control
launchctl unload -w /System/Library/LaunchAgents/com.apple.rcd.plist
brew services start thefox/brewery/cmus-control
- OR -
cmuscontrold

The media keys will launch itunes by default. To prevent that behavior you need to run this command:
launchctl unload -w /System/Library/LaunchAgents/com.apple.rcd.plist

BUT you need to disable System Integrity Protection (SIP) first:
Restart macOS in Recovery Mode (hold Cmd+R while booting up)
Open 'Utilities', select 'Terminal', run `csrutil disable`. To check the status of SIP, run `csrutil status`.
Restart macOS. Open iTunes. Then run `launchctl unload -w /System/Library/LaunchAgents/com.apple.rcd.plist` again.
If you encounter
/System/Library/LaunchAgents/com.apple.rcd.plist: Could not find specified service
it means iTunes hasn't been started yet so the service cannot be found.
Start iTunes first before running `launchctl unload /System/Library/LaunchAgents/com.apple.rcd.plist`