Actually, frying speakers happens when you run an amp into clipping... while driving multi-way speakers. The spurious trash from the clipped signal gets through the crossover networks and frys tweeters and mids because they're not designed to handle that much power, and in real life, there would never be that much energy inside the bandpass frequency of the crossover.
Since the headphone is a single driver device, free of crossovers and anomalies threrof, it should be fine, unless the output devices shorted to the rail and dumped the full rail to the outputs. The outputs of the Beta are Mosfet, which have a negative temperature coefficient, so I doubt that happened, but ya never know...