Without looking up the specs of your Sony unit, the general procedure would be to note the input options e.g. SPDIF and phono commonly appear.
You'd then note the audio output options on your PC, whether from the motherboard's own audio solution - or - from any dedicated audio card you have added to the PC.
SPDIF/digital would be the preferred option, though analogue options (e.g. 3.5mm speaker jacks on PC to phono inputs on Sony) are acceptable (try to keep the analogue cable runs to a minimum and/or use good quality shielded cable - trial and error here since cheaper cable can still give good results).
Which ever option you chose you will need the corresponding cable and connectors - e.g. search Amazon for "phono to 3.5mm 10m" for a 10m cable with phono at one end and 3.5mm jack on the other. Digital cables such as SPDIF can use simple phono leads depending on the plug ends.
You might also need to set/confirm the audio routing on your PC's audio software - so that the 'default' output matches your needs, and, select 5.1 an the output option.
Additionally, if using SPDIF, you might need to match the Sony unit's expected sample rate e.g. 48kHz. Both the PC's audio software and the Sony unit might have options for this.
Lots of resources online e.g. http
/h10025.www1.hp.com/ewfrf/wc/document?cc=uk&lc=en&dlc=en&docname=c00501081,
http/en.wikipedia.org/?title=S/PDIF