based on your drawing, this should work, provided that "star ground" also includes the amplifier PCB and power supply PCB grounds.
one thing though, XLR pin 1 should not be connected here. it should be connected to the chassis through the shortest path possible. how you connect the chassis to circuit ground elsewhere is another story.
as for the metal body of the attenuator, i would have it conduct to the chassis and dont try to wire it anywhere.