Daniel, I found an old Chromecast (version one) about the house and tried your suggestion. The only connections on this model are USB for power and HDMI on the Chromecast itself.
I connected both USB and HDMI to the Denon, connected to my router and it updated itself to the latest firmware.
Then I tried Roon, and it connected and works!
What I have noticed though, is when playing Tidal Masters, the play light is showing green (Hi-Fi) and not white, (best quality). When I was previously connected with the pc directly to the Denon via HDMI, I was getting the white light, indicating Hi Res.
Do you know if the Chromecast is capable of this, and if so, what settings I should alter? Thanks.