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You only need one of them to be able to decode the surround sound, but if you do that in the blu-ray player, then you do need to be able to pass the audio from the player to the receiver. I mention that because not all receivers have the proper connections or processing to handle that. You could do that with either HDMI or multi-channel analog audio connections.
Your receiver can process audio over HDMI, so you are all set. You would need to set up the audio output in the blu-ray player correctly (to PCM or LPCM, I think). If you told us which player it was, we could help you with any questions on that.