Ok, first of all, you meant side surrounds, not "back", correct?
Which leads me to ask you, assuming that you are using mch analogs, that the surround cables are indeed connected to "side surrounds", and not "back surrounds", at both the inputs at Acurus and outputs of Panasonic.
You may know already, but if you ever use a full 7.1 with those mch analogs, you will not be able to matrix from a 5.1 track. Irrelevant for now, but just FYI.
In any case, good luck.