Panasonic HDMI surround system problem

Question

Hi - just wondering as to whether anyone can help me. Just purchased a SC-PT350 - 5.1 Wireless Home Cinema System. Working fine when playing DVDs etc but how do I get it working just on TV only? Have tried selecting surround sound on tv option but then no sound at all? Connected via HDMI cable only - do I also need to connect audi cables to get ot working? I have a pansonic plasma which should be compatible? please help!!