I just got my xprotolab plain from Amazon and have it up and working, but I can't seem to find any documentation for it. The downloadable manual covers the xprotolabs that have a screen and input buttons, but not the headless "plain" version, which seems quite different.? Where should I look for a manual for the "plain" version?

The plain runs (almost) the same firmware. The features are all the same. You only need to control everything from the GUI.