Pro audio mixers are different from DJ mixers because they typically have more microphone inputs and fewer line level inputs. They typically do not have crossfaders or DJ effects built-in, either. Most pro audio mixers have features like individual channel equalization, mic effects, and effect sends. Some professional audio mixers also have sub groups that allow you to assign channels to groups for easily making adjustments to entire groups of mics (like a drum kit).
Also, pro audio mixers are recommended to be used between any DJ controller and the speakers. This is is because pro audio mixers tend to have significantly better sound cards and pre-amp audio output quality.