Yeah, I was talking about the bottom 2 bands, but honestly, if you're not sure what you're doing, you can do more harm than good. One thing I can say for (almost) sure about the C4, if you stick with the "Basic Multi" preset, you won't do much damage, and you'll probably improve your mix 90% of the time. It's not going to drastically alter the dynamic range of your mix, but it will provide a kind of a gentle "mastering" curve...slight boost in the low and top ends, scooping the mix out just a bit. I have to say, your ears should ALWAYS be your guide...use the "preview" feature, etc. If you mix is in pretty good shape to begin with, then the multiband will just tighten it up a bit. If your mix has serious problems, no multiband compression will save it. Well, actually I saved one mix one time, lol...but for the amount of time it took me, I could have (and should have) re-recorded every track in the mix, lol.