About connecting from PC to Sony Hi Fi

[AlphaTester]

Hi, sorry if I posted at the wrong sub. There is a problem which bothered me for a long time. I am connecting my PC to my Sony Hi-Fi with a 3.5mm export > Red White. I think my Hi-Fi only has Red White, Digital In ( TV ) and a LAN port at the back.

However, it appears only front speaker is activated but not the back ones. How can I make it works? It seems there is a rear export on my motherboard export. Do I need to work with this one as well? Subwoofer will be another problem.

There are also SPDIF-6E Out, Hi Fi 6E x 2 at my motherboard but I am not sure if it is related. Will it be like I need to purchase another adaptor, export the Hi Fi to that hub, and then export the audio to red white once again? ( Not quite sure what they are, I just guess it from the name )

Any help is appreciated. Thanks!