personally i do not think that it will harm the system. just set the volume level at acceptanle level on the laptop speakers, plug in the external ones and ajust the level using the the speakers control.
It will not harm the system. All I ever use is external speakers on notebooks. They work great when plugged into a home theater system. Just make sure the external speaker system has it's own power source, since the headphone jack does not supply enough power.
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