One of the codes is default address zero, which will control all tivos no matter what address it is set to, switch each to different codes like 124 and 125. Now cover one Tivo as you make our way through the menu of the other to info screen, let it see a command from the device on the 780 you wish to control it, like right cursor. Back out of the info screen, to main menu, now cover that you do the same for the other TiVo.