Well, you could buy Hubbell hospital ground outlets and then use a copper wire to star ground everything. On the other hand, you have a decent master ground with the metal housings, since they are all tied together. The only ground noise you will get is the ground current traveling to the earth and neutral connection at the distribution box. That is the wire connection you need to be focused on. It might be a thick copper wire or it may not be but it sure isn't zero Ohms! You will develop a voltage on that wire due to the ground currents.