Can my Nucleus control my Anthem MRX 720?

My nvidia shield moves the volume on my Anthem receiver. But, the Roon software doesn’t seem to do the same. Given that I’m going via HDMI out from the Nucleus into my receiver I’d imagine this is easily done.

What setting do you have for Volume control under Device settings? I suspect that the audio signal from the Nvidia Shield is passed through the system mixer whereas Roon has exclusive control of the Anthem.