| A square wave is basically distortion, as a clean signal gets distorted it becomes more and more like a square wave (feel free to correct my anyone) overdrives and distortions clip the signal slightly, where as fuzz turns it pretty much completely into a square wave, as long as you're careful with levels there's no reason distortion should damage your speakers.
As for synth pedals, most synth sounds are achieved through combinations of fuzz, filter and octave effects,some of them can get into speaker blowing territory, a compressor afterward to even out spikes would defintley help avoid that |