I know there are 6.1 receivers. I have one, Yamaha RX-V1. It will use the rear center when the receiver is decoding a DD/DTS 6.1 soundtrack. Those are rare. It will also matix in the rear center with a 5.1 soundtrack. My receiver only has 6 channel analog inputs. It won't use the rear center when I am using those inputs.
What I am talking about is the multi channel analog inputs on the receiver. Do you have 6, 7 or 8 inputs? 6 channel will have left front, right front, center, surround left, surround right, and subwoofer. 8 channel adds rear left and rear right. Maybe you do have 7 inputs but I've never heard of that. I've never seen a player with 7 ouputs.
If your receiver does infact have 7 channel inputs, I doubt it, then you could use a y adaptor on the 5000. That way both rear channels will be played through the one rear channel of your receiver. This only applies when you are decoding a 7.1 audio track. Since there aren't that many movies with 7.1 True HD I don't think it is that big of a deal. If the 5000 decoded DTS MA then I would be more interested since there are more and more 7.1 tracks in that format.