I have an Onkyo 805.
Yes, if using one surround back, use the left surround back input on receiver.
Surrounds, in a 5.1 setup, are the rear speakers. In a 6.1/7.1 setup, they are the side speakers, and the rears are the surround back speakers. If you're just using a 6.1 setup, and the 6th is...