Level setting and tuning... first set your gains correctly then apply the proper crossover settings. And make sure your subs aren't wired out of phase.
Read the attached article, by Richard Clark on how to "optimally" set your gains. You want a 3:1 gain overlap at the amps (more or less to your liking) to maximize system performance with little negative effects to sound quality.
After you have the correct gain structure setup, you can tweak the crossover(s). Good starting point is 100Hz Hi-pass for the satellites, and 80hz Low-pass for the subs. You don't want them all playing full-range because all the speakers playing the same frequencies will cause cancellations, as well as possible damage to the drivers.