Instead of resorting to drilling holes in your precious speakers, I'd go with the somewhat less secure but possibly good-enough solution of
Blu-Tack on the base of your speakers. This method requires that you do not install the feet that come with your speakers. Instead, put 5 pieces of Blu-Tack at the base of each speaker -- one near each corner and one in the middle -- and then affix them to the floor in the desired location. This should prevent them from tipping and shifting if someone whould bump into them. It will not, however, prevent a kid who's really intent on pushing them over from doing so.
If you elect to go this route, I'd recommend playing with speaker placement before applying the Blu-Tack.
I have M22s and used this method to keep them from being knocked over by kids and cats. Granted, my speakers are significantly smaller, but the hold provided was surprisingly strong, nonetheless.
