Probably not a Xerox driver at all if you need to go to an Advanced tab just to do duplex. Duplex is almost always on the first screen:
Basic desktop printers
Typical Office printers:
With EFI Fiery RIP
Another location on the Fiery RIP
And the Freeflow RIP
So not one of the product types Xerox sells seems to place Duplex for the job on an Advanced tab.
And that also applies to OSX, and I can fully discount Linux/Unix since neither is capable of using MS Word
Then, if you are expecting Word to designate simplex/duplex from its own integrated menu system here:
Then that relies on MS software that should be able to pull the information on what the selected printer has via Bi-Di comm to the installed printer, whether that works is another thing. It gets most of that information from here in the driver Properties
But, it would also depend on what the printer is, what driver you have and how it is connected (Wireless, wired, USB)
But assuming the correct Xerox provided driver and not some Generic, wrong, or MS Class driver, it sounds like you have an issue with MS Word.