Optical Chord

Hi, I was wondering if anyone could help me with my set up.

I have an optical chord running from my ps3 to my 5.1 surround sound reciever, and an hdmi chord from my ps3 to the tv. How do I set it so that I can have 5.1 surround sound? Only the front speakers work right now

the thing is, i dont know what to click.

i've played around with it already.. checking/unchecking random boxes. but it still doesn't work..