HDMI cable is expensive!
Im using the extreme mac cables, the HDMI was about 60 bucks from digilife (which is cheap!).
http://www.xtrememac.com/audio/av_cables/hdmi/
So far everything has been great.
I'm only running 5.1 at the moment. I really think the B+W 602 or 603 series speakers are the bomb for the money. As for amp just be sure to go high current not high watt rating. AV shops know the difference.