Rear surrounds are to be added to an already setup 5.1 system. Dolby PLiix or Pliiz uses information from other speakers when a 7.1 track is not being played. You cant really use the rears in lieu of side surrounds. If you want it to be 5.1 with the surrounds at rear which is not correct placement the you would connect to the surround output on the receiver.

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