Tom, as you see, the jack marked "out" can also serve as an input. There's an internal "Y" arrangement, with both top legs of the Y(from input and output)being able to go down the bottom leg into the sub amp.
Note however, that subs don't have an actual internal crossover; the control is just for a low-pass filter which rolls off the sub above the selected frequency, but has no effect on the speakers. If you want to change the crossover frequency between the sub and speakers this has to be done in the receiver. The low-pass control on the sub should be left at the highest setting to keep it out of the way of the crossover that the receiver is doing.
