Could it be that you connected the amp's main power line to the empeg switched power output? Then you're probably overloading something in the empeg. That empeg output line is meant as a control line (with low current, i.e. high impedance on the other side) rather than a high-current power supply. Usually amps have an input connector for this line, and they use a relay internally to switch themselves on or off, depending on the voltage of that control line. They draw the current they need from a separate line that feeds +12V, no matter whether the head unit(the empeg) is on or off. So, check to make sure that the empeg's switched power output is not wired to the main power input of the amp.

Daniel