You will not be able to use a 5.1 sound system properly. To do so you need 3 audio outputs jacks:
1. Center speaker & Subwoofer.
2. Front Left / Front Right speakers
3. Rear Left / Rear Right speakers
You only have 1 audio jack and that is for stereo only.
S/PDIF is audio digital output that uses a different type of jack than the typical 3.5mm jack used by headphones and 2 / 2.1 speaker systems.
S/PDIF output can output multi-channel surround sound, but it must be in Dolby Digital or DTS compressed format. That basically means only for DVDs and Blu-Ray movies. Otherwise you will only get stereo if you are playing games or listening to music; you may not get bass since in a 5.1 / 7.1 audio system it shares a separate channel with the front center speaker.