N
NYMorningstar
Recording Modus Operandi
I'm not familiar with his software but is he using it as a MBC or a limiter?Crossover sets the frequencies where one band starts fading and the next band starts taking over. The crossovers are represented on your graph by the vertical white lines. They basically set the overall width and placement of each of your four bands of compression.
You should learn how to get you mixes to sound good without using Blowzone in mastering first. Then if/when you do decide that you need to use Blowzone in mastering, the results will sound 5 times better than they do now.
G.