Re: Onkyo TX-SR705
I can't really think of any reason why the receiver would not recognize the surround back speakers.
I am assuming that they are connected in phase and that you are not bi-wiring your front speakers.
Do you have speakers connected to Zone 2 or is Zone 2 on? I believe when zone 2 is in use, it uses the watts/channel that are assisgned to the Surround Back Channel.