The quality of sound possible from B&O active speakers is such that it would be a shame to just run a minijack to speakers analog connection from you laptop to the speakers.
There are various soundcards and DACs you can use. (Digital-to-Analog Converters.) Or else you can connect your speakers to a stand-alone receiver which has in-built DACs.
Mac computers (most) have a combination analog/optical minijack out port - you can get an optical Toslink s/pdif signal straight out of them - this signal can then be converted by a DAC which your speakers are connected to. You don't want to control volume using the Mac, as you then engage the laptop soundcard, which is inferior. Most DACs have volume control.
Similarly, with most soundcards you can also control volume. They accept a range of different inputs, with some fitting in the cardport of your laptop, and others connecting through USB or Firewire. Look for cards that have output connectors compatible with those you'd use for the signal connection to your speakers.
I personally use a Grace m902 DAC, which feeds my BL3s with abandon, and provides excellent control of volume.