I believe that the desired results could be achieved by multiple ways, hence would like to privide my inputs as following.
Do check if the 3000 sheet stacker accessory is recognised/configured for the drivers installed with Win7 computers (PCL5 drivers), if not then try to configure the driver manually (go to printer properties and set the accessory hardware as Installed/available).
Installing and configuring universal print driver (UPD)-PCL 6 driver for Win7 computers might help.
if everyone always wants to print to the same destination, then keeping the 'Automatically Select' option enabled for all the users and changing output destination from printer could be a option.