The rotary thing you are refering to is actually a volume control. There should be an input and output side of the volume control. Just run the speaker wires from the zone 2 on the amp to the input of the volume control, then the output from the volume control to the speakers. Most volume controls only support 1 pair of speakers. if you intend to run more than 1 pair you will need more volume controls and a external speaker selector. post back with any more questions.
Peace,
Tommy
edit: I should add, if you want the zone 2 speakers to work you just need to turn it on with the button labeled zone 2 on your amp.