Enable Duplex printing in W7 on Xerox 5500DN printer

http://forum.support.xerox.com/t5/Printing/Global-Print-Driver-Phaser-3635-Cannot-Duplex/td-p/2078

I suppose you share the same problem in different products.
I have tested the Global Print Driver (GPD) PCL6 and I am able to print duplex.

After you install the GPD (Pointing to the correct IP address) make you go to properties > Options > Device Options > Configuration and select the correct printer model. Very likely what you have is "Basic Print Mode" and you need to specify your printer. Make sure you click Apply and ok to close the Printer wizard.

If this does not solve your problem you can also try to go to Properties > Configuration and disable Bi-Di. After you hit apply and OK you should have Bi-Di disable wich allow you to enable and configure the printer options manually. ( Driver Properties > Configuration > Instalable Options.

@hirize,
In your case please consider all this process with the GPD PS driver. Due to the nature of you printer. Very likely you will not be able to change the print mode for this phaser on the PCL6 Driver.