@mahcneto
You might try testing with a different HDMI cable.
When you plug the Raspberry Pi directly into the TV does it have sound?
You can open up the audio mixer by typing alsamixer from the command line and make sure the volumes are up.
Do you have a 3.5mm cable you can test with? Plug that from the Pi's headphone out into the Input port on the Avermedia LGP and see if you have audio? If not type in this from the command line when you SSH into your Raspberry Pi amixer cset numid=3 1 and then test the audio again.
You can force it to HDMI audio out by typing amixer cset numid=3 2 from the command line.
Another solution is updating the firmware for your Avermedia LGP and trying again.