I would worry more about damaging your ears. Eton drivers are only $200 each or so. Your ears are priceless. As a rough estimate, try talking at a normal volume level, as if you were talking to someone else in the room. If you can't hear your own voise very well, the music is really loud.
As for your speakers, it is very frequency dependent. The more very low frequency content, the less loud you can play them before they reach their limits. there are at least 2 ways to damage a speaker - emlting the voice coil and bottoming out the voice coil. I'm not swure there's a good way to tell your overheating the voice coil until it's too late. If you hear a buzzing sound or a loud crack on loud deep bass notes, your hitting the voice coil against the magnets, and are at risk of bending the voice coil and ruining the speaker.
As for your speakers, it is very frequency dependent. The more very low frequency content, the less loud you can play them before they reach their limits. there are at least 2 ways to damage a speaker - emlting the voice coil and bottoming out the voice coil. I'm not swure there's a good way to tell your overheating the voice coil until it's too late. If you hear a buzzing sound or a loud crack on loud deep bass notes, your hitting the voice coil against the magnets, and are at risk of bending the voice coil and ruining the speaker.