I have 5:1 surround speakers and only one terminal for a Surround Back speaker, not two for left and right. Surround left and right are able to mix with the SB speaker. Is this correct? Is there a way to set up left and right Back speakers? Can I (should I)connect 2 speakers to one terminal?
Not knowing what you are connecting the speakers to (ie av receiver or home theater in a box) I would suggest that the device may be a 6.1 channel setup and has surround as well as surround back. Hook your rear speakers to the surround L/R speaker terminals and when you go through the setup select none for surround back.
I would not suggest hooking 2 speakers to the terminals unless the speakers and electronics are matched and the manual says it is OK.