I've got a Phaser 6121MFP printer connected by USB to a Windows XP Pro and shared to the network (full control garanted to Everyone).
Windows XP printer's driver works perfectly: Infact it allows to print documents with 1 side layout or 2 side layout ...
The problem arise when i use the same network shared printer by a Windows 7 x64: in the printers driver property the combo control used to set 1-side or 2 side printing is disabled. All the other controls works: only 1-side or 2 side printing is disabled.
yes, normally the driver is communicating with the printer directly, since you are sharing with usb , that maybe not possible
if you open up the driver properties, in one of the last tabs you can override settings , like finisher options, trays als also duplex unit... you can enable it there