Most household systems have a 1v sensitivity, while PA/pro systems need something near 3v. In both cases, the input at the crossover is the same. Therefore it exlains the much higher gain of a "professional" crossover. You may want to reduce the input level at each of the amps (at least by half), and turn that knob a bit more on your preamp. That should solve your problem.

It would be great if manufacturers could include a switch on the back to select your output. 1v vs 3v.

No experience with the DBX unit.

BTW The DCX is not exempt of faults. My first unit had the dreaded frying egg floor noise and was replaced within 3 months. I suspect I was sold a refurbished unit. The second one I got works perfect. That problem is also very well documented and can easily be fixed.