E-Z Anchors hold incredible amounts of weight as long as the object is not going to be experiencing any side to side movement pressure that could loosen them. QS8's are not for bass so I doubt there would be any vibration capable of loosening things. There is certainly no tell tale drywall dust under my wall mounted QS8s with E-Z anchors.
Still, since I don't want to be blamed for a fall so maybe toggle bolts are a better choice for a ceiling application. I think E-Z's would hold but since toggle bolts are not expensive, why not erase any doubts. Again, make sure they are tightened to avoid any movement that might wear into the drywall.
