I have Three amps. Brax X2000, Arc Audio CXL2500 and Tru TO-3 4.150. Up front I am running a pair of Focal KX 7" w/ Focal tn52 tweeters. In the rear I am running 4 Focal 6.5" polykevlar mids with a pair of tn52 tweeters. The subs are Focal Utopia 27wx 11"(2). The mids are rated to run down to 50hz, but I am not going to cross my subs at 50hz. Here's the question...At what point should I cross the mids and the subs? I am using a sealed sub box of 40 liters.