Welcome.
Don't worry about 9.1 and save your money. The good thing is you already have a 7.1 setup so wall mount the QS8 on the side walls for surrounds (5.1) and wall mount the Diva 3.1 bookshelf speakers where the QS8's where on the back wall for the "surround back". The QS8's don't need the same spacing as they are non-directional so they are perfect there on the side walls. You also want the QS8's as side surrounds instead of surround back because you will want them to get the majority of the surround portion of the soundtrack. As for the Diva's they are more than adequate to use as surrounds with the Diva front soundstage.
