Sorry to hear about your frustration, Craig. I feel your pain.
It could be a very good thing that you could not get that screw to go in where you wanted - it is entirely possible that what was stopping your screw was a cast iron drain (waste) pipe. Or maybe even a galvanized water pipe.
The problem with the FMB (as I understand it) is that rather than the sheetrock simply having to hold it "up" (sheer strength) or "in" (pull-out strength), the mounting also has to allow for the levering force exerted by the fact that the weight of the speaker is cantilevered out from the wall. It's what makes the FMB such an elegant solution, but your trials show that "installation" is more than just putting objects where you'd like them.
I'm hypothesizing that a "plate" (piece of wood like I saw behind some QS8's earlier today...) mounted to the wall with wall anchors and THEN the FMB mounted to that plate might have stabilized the situation somewhat. But you still have to be able to get the drywall anchors where you want them, and it's certainly less elegant.
I'll bet it sounds great, though, doesn't it?
