Coax to an audiophile means RCA. I know you aren't using this since the audio connectors are all 3.5mm and there is no Digital Out.
6 x audio jacks (Center/Subwoofer Speaker Out, Rear Speaker Out, Side Speaker Out, Line In, Line Out, Mic In)
Whats plugged into what? Just describe using jack color and what is plugged into it. Does your 5.1 system have a separate controller (head unit with master volume, gain, sound modes)?
I know what setting you are referring to now. I have this on my Asus Z68 with Realtek chip. Are you selecting 5.1 as the output mode for playback on the interface?