Sound via HDMI

hello all

i have a small problem that i hope someone can answer, i have a new windows 8 laptop running the frodo xbmc now it runs smooth as butter but wanted to hook my laptop up to my tv so i may watch my content stored on the big screen, i have connected the hdmi from my tv to the hdmi port on my laptop and within seconds nice crisp display comes up checked out windows media just to check the sound and worked like a charm that's until i tried xbmc once again the picture is perfect but all of the audio is still coming form my laptop now i tried a few methods to get the sound to come from just my tv but it time im i am met with a fail!
each time i connect via hdmi i get a small pop up asking me to config the default audio device which i set as the tv but as soon as a movie plays all audio comes from the laptop again not the tv i cn even set the volume to 0 and still no tv audio

please can anyone help

thanks in advance