If you go into the menu for "Direct mode" (on the 3808 it is under Manual Setup > Audio Setup > 2 Channel Direct/Stereo) there should be an option to include a sub.
Going there in the menu shows: Setting: Basic SW: Yes Subwoofer mode: LFE x-over: 80Hz Distances: 12.8', 12.9'
So I am good there. Like JohnK mentioned, I was mistaken and had overlooked that 'Stereo' mode includes the sub and is the mode to use if I want 2 ch + sub.
Dave
"In theory, practice and theory are the same. In practice they're not."