Hi Bruce,
Please use the Roon Ready “connection” which is part of your ethernet LAN. It has the best audio performance (by quite a lot) and also makes full use of the Roon Ready integration features.
Simply Enable the Altitude16 in your Roon software as an Audio Zone. The rest just works.
If you want to use the Roon HDMI video interface, select that HDMI connection and then select the Roon Ready connection (either from the Altitude or from Roon). The video will remain on the last-selected video connection, while the audio will move on to the Roon input (which utilizes our excellent clocks rather than being limited by the quality of the clock on the incoming HDMI connection).
Best,