Need Sound With System

Just got a Panasonic sound system to go with the Optoma HD 720.

I have the wii hooked up to a Sonic reciever system with multiple outlets

The optoma is hooked up to the Panasonic sound system and I can watch DVDs with sound.

Here is the issue: I can play wii but don't have sound, am I missing a connector that plugs the sonic reciever system to the sound system?

The panasonic system came with a yellow cord and I plugged that into the panasonic and the sonic, but no sound

Thanks for the read