Sounds like you are just installing the PPD but not applying it to the printer. Check if the printer is using "Generic PS" or similar for the PPD.
If it is, then that is your issue, install again, and when the dropdown for "Print Using" appears in the OSX installer wizard choose the 6000 PPD.
I just bought a new MAC and my Xerox Phaser 6000 printer was installed with no problems, but i can't acess any configurations of it...and it's printing bolder than it was on my old PC.
I've already tried uninstalling it and downloading the driver again, but i still can't properly configure it.