...The problem is that the driver (even the last one) doesn't have such tab. No way to manually add duplex unit...
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
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.