I have just purchased the Panasonic TH37PX80 and the Yamaha DSP-AX763 av amp amd am trying to work out the way to rig the sound from the tv to the amp ,at the moment they are connected by a HDMI cable on the AV amp output and there is no sound through the amp ,can i get the tv sound through the HDMI out or do i have to use a seperate cable from the tv.