For extended seating arrangements with two rows you should place L/R Surrounds to the sides of the 2nd row seats and then place Surround Backs at least 4' apart or more depending on your room.
But if I had such a setup I would do what the theaters do which is multiple L&R Surrounds that share the same input signal. But for the Majority of people here 7.2 is more than capable for our needs.