What do you mean by one single sub.. do you not have two separate subs?
If you do have 2 subs then I believe you just run 2 speaktrons out of the amp, one for each channel. you only wire the first channel to 1+/1- and you wire the second channel to 2+/2-
(edit: My experience is limited. I have a single sub run off of my EP4000 in bridged mode so that 1+ is positive and 2+ becomes negative out of channel 1, and I just run a single wire to the sub)