You can try fining the TV input problem by adding a Chromecast capable device on a different HDMI input of the AV10. The Marantz has the capability of teaming inputs and can process the audio from one port and the video from another.
I have an older model Marantz, and does not let you team HDMI inputs, but current Marantz features seem to support it. While playing Roon, press the options button on remote and activate the “Video Select” feature then choose another active video input. You can test this with any other video input you currently have.
Here is the link to the Marantz Video Select Feature