Sonos 5.1 with mysky and ps3

Hi there

I have a sonos 5.1 hooked into my tv with an optical cable and my my sky and ps3 connected to the tv with hdmi.

The sonos only seems to pick up stereo even when I am playing a bluray on the ps3. I suspect the problem might be my tv may not pass through 5.1 (it's a panasonic th-p59g).

Any suggestions of the best way to set it up for 5.1?

Many thanks

Mike.