I agree that this is frustrating. Like jmartin225, however, I have been able to open the Hardware panel in EVERY instance by selecting an input channel in the mix console, sometimes turning the visibility of various channels off and on a few times, double clicking in random places, etc. and VOILA! eventually the Hardware tab will become visible. The hardware control functions on the mixer input then work as usual, and you can open the elusive Hardware Settings dialog box by clicking on the headphone icon at the Left side bottom of the hardware secion of the mixer input channel, even though it still does not appear in the Device menu as it should.
I must admit it’s a bit embarrassing to do this in front of a client. They are probably asking themselves why I don’t upgrade to actual working software with the money they are paying me. 
This functionality is essential, as Cubase also randomly “forgets” which outputs I have assigned to the MR816 headphone outputs and this is the only place to reset them, in what appears to be another little annoying bug. It was a major annoyance (couldn’t get the client’s mix right, no levels would change) until I noticed what was happening. “Can you give me less Banjo?” “Well, not at the moment!” 
BTW, direct monitoring (zero latency) is set in the VST Audio section of the Device Setup menu, not here. That is not affected by this issue.