Are you saying that you experience audio drop outs when Foxtel is connected to the TV with HDMI cable AS WELL AS when you are using optical to amplifier ?
Any audio drop-outs through surround sound system when you are using optical ?
It could be an issue with HDMI cable ...
The first thing you need to do is try different HDMI cable, ideally 1.3b version.
Have you tried to connect other equipment to the same HDMI input ?
Bookmarks