I wondered about the 5V, not a big problem, a simple DC supply fixes that. I was just looking at the AD-20 and realized that it probably didn't have it's own 5V, no components to supply it. I looked at the AD-20 as a quick way to receive the serial data and provide the decoded backup light and coupler outputs.
I perceive the greater desirability to use the IR tether to be ERR TMCC upgrades, that's what I'd like to address. I have a board design in progress that will do the whole job with one board, handle the IR receiver, decode the serial data, and buffer the serial data to the ERR RS Commander board.