I got it.
This is what i did:
1) Delete these Files by hand:
USB
/Applications/Fireface USB Settings
/Applications/Totalmix
/Library/Extensions/FirefaceUSB.kext /Users/username/Library/Preferences/de.rme-audio.TotalmixFX.plist /Users/username/Library/Preferences/de.rme-audio.Fireface_USB_Settings.plist /Library/LaunchAgents/de.rme-audio.firefaceUSBAgent.plist
Thunderbolt
/Applications/RME Thunderbolt Settings
/Applications/Totalmix
/Library/Extensions/RMEPCIeAudio.kext /Users/username/Library/Preferences/de.rme-audio.TotalmixFX.plist /Users/username/Library/Preferences/de.rme-audio.RMEThunderboltSettings.plist /Library/LaunchAgents/de.rme-audio.RMEPCIeAgent.plist
2) Reboot
3) Go to System Preferences - Security
Switch App-Download to App Store
4) Reboot
5) Download UFX+-Driver and Install. If promoted, click "allow".
6) Reboot
7) Go to System Preferences -> Security and allow RME Software to be opened.
Done! :-)
Now you can switch Security Settings back to App Store and verified Developers, if you wish.
Frequently in use:
Fireface UFX+, Fireface 800 (as a AD/DA-Converter) and an old RME Sweater... ;-)