I have found that the Postscript option has to be enabled with a code that is unique to that printer's serial number. I had to acquire mine through calling the support. If you look go to the CentreWare Web page and search in the Properties tab and then Services/Printing and then Page Description Languages, you should see PostScript in that list. You will see the alternate driver languages:PCL, TIFF and XPS.
I was recommended that the PCL driver on your computer however will omit this issue if the PostScript if that is not listed. Otherwise you have to call support to acquire that specific code.
Postscript isn't free, if it was free, it would just work without a code.
If someone called Xerox support (not sales) and was given a key, it would have to be that they had the code already, misplaced it, but had installed it long enough that it registered on Xerox's servers.
In that case, some Xerox support people can retrieve the information from the Serial number of the device.