This guide describes the steps to opening the case.
Remove 2 screws from each side of the amplifier.
Remove 2 screws on rear of device. Slide top cover up and back from main case.
Remove 3 screws on bottom of case.
Remove 13 screws on rear panel.
Using a pair of pliers, squeeze the retainer for the power cord as shown and pull it toward the external side the panel.
It may require some wiggling, but it should slip out of the hole and then off of the cord.