I agree, although personally being a perfectionist I would want the QS8's at least point mostly towards the seated area, although in reality at movie listening volume it probably doesn't make a whole lot of difference.
As far as the center goes, if you can put it above, go for it. Nothing wrong with that at all. The only disadvantage I can see is if you have carpet, you'll get more reflection off the ceiling if it's above as opposed to the carpet (none) when it's mounted on the bottom. If you have multiple rows of seating like a theater type seating, on top would disperse better to the back row.