Aaron’s Home Audio Tips for the night:
You get absolutely no advantage using an HDMI cable like this:
http://www.gspr.com/wireworld/ps_hdmi.html
Expensive optical cables also have no advantage. At the minimum all you need is a cable that doesn’t fall apart.
Theoretically, higher quality speaker cables *can* improve sound, however the improvements are most likely outside the realm of human hearing. There have been comparison tests with using coat hanger wire vs. using a high-quality speaker wire and listeners were unable to tell the difference.
My recommendation for any of your cable needs:
http://www.monoprice.com