I am in a metal band and we have bene together for a few years now and are starting to headline most of our shows, so there for we must provide the PA system if there is no house PA. We have a small powerd mixer and some good dual 15 JBL's, these work great for vocals, but is not big enough to be able to mic the drums, amps, and what not. We are wanting to purchase a good size PA system, and i was wondering what all i will need. I know i need a nice mixing board, were wanting around a 24 track. And about a 2500 watt amp to run it. Where im kinda mixed up is about the rac mount gear, such as crossovers, preamps, and all of that stuff. Could someone inform me on what these things do, and if they are nessasary to run the PA, and what i will need to buy to get good sound from the PA. Thanks You very much.