Hi, ok, so, has the amp got HDMI connectivity on the back? If it has then you may need to use the ARC channel, if it has it!
If not, then try changing the sound output setting to another mode, like all channel stereo mode and see if that produces any sound.
Sometimes if the channel you are watching is NOT outputting surround sound of the chosen mode, it will not produce any sound.
Let me know how you get on!
K.