Hmm.. my manual is from 2014 and states on page 11, step 8...
"Using included harness, connect DD-1 to output of amplifier. Connect the red harness lead to the Speaker (+) terminal, connect the black to Speaker (-) terminal."
It detects the 40hz signal, and detects distortion when I turn the gain up too high... but just wanted to make sure it made 0 difference as the gain is a good bit higher then I previously had it set.