Yes, there is no reason you can't feed a Roku TV with a Roku player. I did it myself with my Sharp Roku TV and my Ultra for a while. For your situation it would seem to be the best solution. Just remember that the Ultra and your TCL TV are 4K capable. If your upstairs TV isn't 4K, make sure you set the Roku Ultra to 1080 output. If both TVs are 4K, make sure your HDMI splitter supports 4K 60p and HDCP 2.2. Be aware that 4K Roku players can be extremely sensitive to HDMI HDCP 2.2 connection issues.
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When you plug something into an HDMI jack, you can rename the input from a selection of names. Roku Player is one of the name available, so Roku obviously considered this.
Dan
Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.