I have a Yamaha RX-v1 receiver and a pair of polk audio rti10 speakers. what...

...should i set impedance to? The yamaha RX-V1 has an Impedance selector switch on the back of it. My RTi 10's are my only speakers and are connected to the reciever using the Main A and B inputs. the speakers each have two inputs on the back so i am using 2 channels on each speaker. So, what should i set the impedance switch to? Please help as i do not want to damage my stereo or speakers. thanks a lot. Chef Luis Pernia