I think I got it figured out. There already exist a UCI interface for every emulated old chess computer. It's written in lua. This is how Arena can communicate with the chess computers in UCI. I just need to figure out how I can use the keyboard (console) to send and receive UCI data. For example, if you start the Stockfish engine from a command line, you can communicate with it in UCI. How would I do that for the old chess computers? E.g. if I open a command line and type "messchess boris" the emulated chess computer starts up but I don't have UCI communications from my keyboard.