How do I get sound using HDMI cables with my XBOX360?

I have an XBOX360, and a Sony multi channel AV reciever STR-DA500 with HDMI hook up. I hooked the HDMI cable to the 360 and into the BD connection to the Sony reciever. From the reciever I plugged the HDMI cable to the TV. I have a wonderful picture but no sound. I noticed that the reciever has optical conectors for the BD port but how do I hook up sound to come out from the reciever. And if I need the optical cable to make it work how do hook an optical cable to the 360. I feel like I am loosing here unless there is a reciever that plays sound from the HDMI cables alone. I do not know what to do. Please help and let me know if I need to make my question more clear.