There is a known issue with the latest RME drivers for Windows (v. 1.114) affecting Reference Systemwide and Measure software.
If you get the following error - "Audio error! Couldn't discover supported formats" in Systemwide settings when selecting your RME as the output device, please uninstall your RME drivers and download the previous version from here. This should fix the issue.
Installing the previous version of drivers will also fix the issue on Measure software when selecting your output channels. If the problem persists, please contact support.