Why do I get such bad interference when I connect my Macbook Pro to speakers with a stereo cable?

I have a 15'' 2011 MacBook Pro and when I try to hook it up to my stereo system there is almost nothing but static. I have tried both Belkin and Auvio cables and the same thing happens with both. When I hook my iPhone 4 up, both cables work beautifully. The stereo is a "Cyber Acoustics CA-5402 Platinum Series High Performance 5.1 Speaker System"