Are you passing audio through the TV?

I will skip duplicating prior discussions about HDCP and what that means to passthrough of HD content but to get this to work we connect like so.

Source -> HT (Denon or such) -> HDTV

That way the HT can process the audio and pass the HD video to the TV. Due to HDCP you are never sure to get HD Audio out of a HDTV. Many folk have lost years over that issue.