headphone outlets tend to be lower volume, you don't want to blast your ears with as much as you put out into speakers.
but most powered speakers have a built in amplifier that will compensate for that.
You are not going to damage anything, so i would just plug them in and see how loud you can make it.
you may need to also adjust widows volume control, as well as the speakers volume control (if they have a separate control)
John