Speaker Configuration problem for Windows 8.1

I recently bought a Sony Av Receiver and with some Wharfedale speakers.

I have my PC hooked up to my TV in the living room.

I decided today to configure my speakers in order to achieve 5.1 surround sound in my living room. So i opened up the speaker setup within Windows and chose 5.1 out of the list that was there.

When i press test, i could hear audio from the front left, centre and front right speakers. No audio from the rear speakers and subwoofer. In fact the audio which was intended to come from the rear left speaker instead came from the front left speaker. And the same happened on the right.

This is my cable setup: I have a hdmi cable coming from my graphic's card in my pc to my TV and an optical (spdif) cable coming from the TV going to the AV receiver. On the AV receiver display it says Linear PCM when connected.

I've searched google for a solution but to no avail.

Please can somebody help me with this, i don't know how solve it.

Thanks in advance.