Disconnect your crossover from any power source before connecting anything to it. Make sure your source device and power amp are both turned off.
Use TRS or XLR cables to connect the outputs of your source device to the inputs of your crossover. Follow the markings on your devices carefully.
Use TRS or XLR cables to connect the inputs of each of your power amps to the appropriate outputs on your crossover. Likewise, connect the outputs of your power amplifiers to the inputs of your speakers.
Turn your power amplifiers on, and turn their outputs all the way down.
Connect your crossover's power cord to your crossover first, then plug into a grounded power source. Turn your source device on and turn its output level up or down such that you are sending a nominal (average) level to your crossover.
Turn up the outputs on each of your power amplifiers and adjust until you achieve your desired volume.