If you want a quick/easy/hacky way to do it and have iTunes ... add all the songs to a playlist in iTunes and make sure that you've enabled "Sound Check" in the iTunes preferences before you burn the audio CD ... it does it's own level comparison and tries to match up the sound levels in all the tracks. Not sure exactly what it does to be honest, but it does a semi decent job of things if you're not looking for re-mastering quality ...
Mark