To assign the controls of your SL MK II to parameters within Mainstage, firstly open Automap and in the Settings Menu, ensure that the MIDI Input Port and MIDI Output Port are set to 'Automap MIDI.'
Within Mainstage, select a New 'Keyboard Starter' Template and drag into the blank space all of the controls you would like to use (here I have created all available controls for the Remote SL MK II - Mainstage template file and Automap Template attached to this article).
You can change the size and aesthetics of the controls to suit your preference.
Now Select 'Layout' in Mainstage and click on a single control to highlight it in a blue box. You will notice that the Hardware Input settings appear on the left. Set the Device to 'Automap MIDI' and the Channel to the relevant Channel you have selected in Automap - here I have used Channel 1. Now click on 'Learn' (turning the blue box surrounding the Mainstage control, red) and move a knob or press a button on your Controller. Repeat these steps until your controller is assigned to this template.
You can now load various patches and control them as you wish in Mainstage with your SL MK II.
Attached to this article is the Mapped out SL MK II Mainstage file.