Lift the midplane assembly out of the front case.

Be mindful of the inverter cables on the hard drive sie of the midplane that may get caught as you lift out the midplane.

During reinstallation, insert the screw heads protruding from the speakers along the lower edge of the midplane into the holes in the front bezel and thread the inverter cables through the openings in the midplane before lowering the top edge down into the front bezel.