The question was asked about digital signage hardware since most manufactures of that hardware have thought about how to control the TV along with outputing the content.

I looked up the TV he has listed and it is a 42" smart TV w built in apps. I think he is trying to have each TV internally play content from a networked location like you would in your house. You have 2 options unless the TV supports IP control, walk around to each TV with the factory remote or spend the money on a routable control system w your choice of user interface. Whether that is pc based, tablet (ipad) based or handheld remote control based. Any type of solution will cost anywhere from the price of one or two of those TVs to doubling the cost of the overall project.