Re: Grounding 2-prong-wired gear
There is . . . buts its not quite as straightforward as you might think. And I don't want to walk you through a procedure that might kill you if done wrong.
But there is a simple alternative:
Plug in the Marantz. (Nice amp, btw.) Turn it on. Hold your hand so that the very tips of your fingers touch the metal of the face plate. Using a very light touch, slide your hand sideways on the metal of the faceplate, so that you are just barely dragging your fingertips across the metal.
Reverse the plug in the wall socket, and do it again. In one direction, your fingers will slide smoothly. In the other, you'll notice a slight vibration in your fingertips. Note which way the plug is in the wall on the way that did not produce the vibration.
Make a mark of some sort near the prong that goes to the small sized outlet hole, and always plug the Marantz in with that orientation. You now have the same degree of electrical protection as a three-prong cord.
btw - if your fingers don't "vibrate" in either direction, its a well designed unit that won't really benefit from a three-prong cord to begin with.