Joel,
Those extra outputs allow you to remove any sound or group of sounds that you choose from the mix outs and give them their own dedicated outputs. For instance, let's say that the bass sound that you were using requires some eq or other effect...you could map it to either Dir 1 or Dir 2, then out to one of your mixer's individual channels leaving the rest of your mix in the mix outputs. In the studio, this is essential, where every single instrument is recorded to it's own track(s).