Am I right that it’s not possible to group these? Why is that when iTunes can do it?
Zones can only be grouped in Roon if they are of the same type. The Roon Output Zone on an iMac running Roon is a RAAT Zone. An Apple TV is an AirPlay Zone.
iTunes uses AirPlay throughout.
Is there some kind of work around be creating a second zone for the iMac set to Airplay?
Under Connected to this Mac I have my USB DAC as a seperate device that could be enabled. Could I make that the core and then make the mac system output an airplay device?
This KB page sets out the Roon Architecture, explaining what Core, Control and Output do. The Core does the heavy lifting and needs to be on a computer.
This KB page sets out more information about Zones.
I don’t know enough about Macs to say whether you can configure a Roon Output as an AirPlay Zone. I’ll shift the thread to the AirPlay section and see if anyone knows.
@Richard_Bailey: You can install software like AirServer on your Mac – this will turn your iMac into an AirPlay receiver and make it visible as an AirPlay zone in Roon (Gaylord is my MacBook Pro - don’t ask ;-)):
Once enabled, you can group the AirServer/iMac zone with your Apple TV (you may want to disable the Roon/RAAT zone for the iMac to avoid confusion – or name it differently, say ‘iMac-Roon’ and ‘iMac-Airplay’).
Not sure how well the AirServer zone performs when grouped with your ATV over Airplay, but I guess you will be fine. AirServer has a 14 day trial for you to find out.