i love toggle bolts and use them for everything. but in this situation i might worry because the toggle bolts are to close together that they may be putting to much pressure on a small area of sheetrock. i would cut the drywall and install a 2x4 then mount to that. because you are not only risking the speaker but also the tv if it falls. just my opinion also i should add i am lazy and i am always looking for the easy way out but in this situation i probably would not.
Jake

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Leave the gun, Take the canolis.