Firing flash strobes in a dark room is a sure fire way to damage your talent's eyes. The extreme light flooding an iris that is adjusted to the darkness, even if it is very low ambient, can be painful and damaging. Be careful about this. Always use the modeling lamp on your strobe to help ease the light transmission to your talent, or they should have their eyes closed if using a dark room.
As far as syncing, Pocket Wizard makes the MultiMax transceiver that allows for syncing multiple cameras and flash strobes. You can set millisecond delays to pull everything into sync with your slowest camera or flash.
The black band is shutter sync related. Usually you can push it to 1/200 or 1/250 depending on your lights and camera equipment. The millisecond difference of firing a slave camera from your main camera can cause the delay. We're talking about the speed of light here, so all cameras must have their shutters open at that very same moment the flash is hitting your subject.