The HDMI switching hardware in these Rotel models predates 4K technology and so unfortunately these Rotel products cannot pass 4K video signals and cannot be updated to support this.

If you wish to use 4K video with these models, consider running the HDMI video directly from your source device to the TV, then if the source device offers dual HDMI outputs you can run a second HDMI connection to the Rotel processor for audio, or if this is not an option use a different connection such as Optical for audio.