One doesn't use the Windows print setup for Gerber printers or plotters. You install each through the GSP Tray. Once done the procedure for outputting a job is also different ...
From Composer you either Output All (Shift +F11) or Output Selected (Shift +F12+. This then will open the Gerber GSPPlot program where you can control all the print and plot parameters of the production of the job. Once you are setup in GSPPlot to run the job, you simply press F10 to send to the Edge and F8 to send the job to the plotter (after you align the printed target with the plotter bomb sight).