If the external speakers supports a toslink connection, and if the laptop supports Dolby Digital Live or DTS Connect Live, then you can use the 3.5mm port on the laptop in Digital mode with DD Live enabled to send it to the speaker's DAC / decoder.
If it doesn't then you will need a USB external soundcard with 5.1 analog output, like some of the Creative offerings.
You'll need three 3.5 mm jacks to run a 5.1 setup (6 channels - 3x2). The laptop has one 3.5 mm combo jack (stereo + mic). The more elegant solution is to use the HDMI port to output both video and 5.1 audio channels.
Since your speaker system only supports 3.5 mm (check if you also have optical input), you can consider purchasing an HDMI Audio Extractor with 3.5mm and optical inputs which costs less than US$20.