How's your Blu-Ray player connected? If via HDMI, then ensure the settings are correct on the Blu-Ray player and amp and also ensure you have selected the Dolby TrueHD soundtrack from the film's menu - quite a few early releases defaulted to the Dolby Digital track and you had to manually change it to the TrueHD track.
If you're still having issues, let us know which Blu-Ray player you have.