Here is a look at the at Power Amp Assign Menu.
This allows you to assign the amplifiers of the RX-V667 to a specific speaker configuration.

7ch Normal is used if you are using either a standard 5 channel or 7 channel setup with no Bi-amping or Powered Second Zone. When this option is selected, and you use the YPAO automatic speaker setup system, it will detect whether 5 or 7 channels are being used.

If using manual speakers setup and only using 5 channels, set the surround back speaker option to NONE.

7ch + 1ZONE means that you intend to use both a 7 channel setup in your main room and an additional 2-channel zone in a second room. In this case, when the second zone is activated, the main zone automatically goes into 5 channel operation.

5chBI-AMP is used when you want to use re-assign the surround back channels (channels 6 and 7) to provide additional power to the two front left and right channels. In this setup, you must use speakers that provide Bi-amp speaker connections, you cannot use this function with just any set of speakers.

For a further look at speaker setup, proceed to the next photo....