While I’d like an integrated option, there are other solutions to make your PC/Mac into an Airplay receiver. Airfoil being one of them for OSX/Windows, Shairport for Linux.
If you don’t set your audiodevice to exclusive mode they should work together.
For the Linux server there should be an option to pause Roon (and release audio device) from the commandline so Shairport can take over if needed.