I’m not sure what your question has to do with Neil Young. I may be mistaken, but it seems to me that your question amounts to “There’s this streaming service that I can access from my iMac, which is not supported by Roon. How do I stream music from that service to my RPi Roon endpoint(s)?”
The answer is “AirPlay”. On your iMac, you can redirect the sound to any (combination of) AirPlay receiver(s) on your local network.
So now, the question becomes, “Does my RPi Roon endpoint speak AirPlay?” If you installed RoPieee XL, then yes it does. That distribution comes with a program called Shairport-Sync, which turns your RPi into an Airport receiver.
(You should be able to see this already in Roon. In addition to its native RAAT protocol, Roon can also stream over AirPlay, so if Shairport-Sync is active on your RPi, you’ll see it as an available AirPlay endpoint in Roon.)