Nick;
I don't have any Atlas engines, but have quite a few Lionel TMCC engines that I have lashed up. After you create the lashup in the Cab-2, as has been suggested, hit the info button until you get to the sound page. There are several choices (Railsounds 4, 5, Legecy, etc.). I would check to be sure that the info screen matches whatever sounds the Atlas engines come with.