When you are there, keep in mind they have 3 runways so when you are monitoring, you will have a lot to listen to. DAL also controls all the ramp channels (once the a/c goes to ground, they get handed off each "concourse" - terminal for gate directions). If I were you, I would just plug in Tower 125.325 (if landing 8R/26L) or 119.1 (if landing 8L/26R) and Ground 121.9 (both runways), else that or you will just be overloaded with air traffic!
Myself and a few others here are regulars on the South parking deck where we get an awesome view of 9/27. Click
HERE to see some of my photos from ATL (I go by mm505 at FenceCheck).
Definitely bring your camera with you as the Aviation Package will offer you photo opportunities that you won't believe!