An extra set of bac surrounds or front high speakers?

I'm getting ready to get a new 7.1 Receiver and I have discovered that the receiver I am getting offers the normal 7.1 with surround and back surround speakers but it also offers the options of Dobly Prologis IIz that will allow me to have the option of an extra set of front high speakers? Has anyone tried the front high speakers? Would this provide a better movie experience that having 7.1 Surround?

Their coming with the home theater set-up. I'm looking at the Onkyo HT-S5300.