Sound problem HDMI-picture and sound by amplifier

I got a sound problem connecting a MacBook Pro to a Flat screen tv by HDMI using the Mini Display Port with an adapter to HDMI and connecting the amplifier by the headset port. The amplifier got a noise as soon as the HDMI connection is made. Although the sound of the television was reduced to zero and the tv located at 9 m distance.

The same happens connection the sound by the speaker port.
The MacBook Pro is running with MAC OS X Version 10.6.8, QuickTime Player.

How to get clear sound using the amplifier?

Firstly the 2 Ports are Headphone/Line Out and Microphone / Line in, you don't want to be plugging the auto cable in the microphone port.

MiniDisplay > HDMI adaptor > TV
Headphone/Line Out > Amplifier

System Preferences > Sound > Output > Line Out