I have two different TCL Roku TVs with Roku devices connected to them and two Voice Remote Pros controlling the power/volume of the TVs. One uses IR and the other uses CEC. If you haven't tried "CEC setup" under "Set up remote for TV control" on the Ultra, give it a try.
You will still need the TV's remote to change the TV's input or for antenna channels. There's no way use one remote to control both the TV (other than power and volume) and the Ultra at the same time. If you get all your content through a Roku device, you can set up the TV to always power on to the Ultra's HDMI input.
