The other posters are right, as another Australian with a keen interest in AV, some products are a lot less viable to buy over here than in the US. Some general advice, there are some good value Australian speakers around, and they are usually better value than imports due to lower shipping costs (google Aaron, Adelaide, Richter, Subsonic, Legend Acoustics, and Whatmough for some ideas).
As for the rest, you'll probably end up either buying it locally, or importing suitably. The Emotiva gear is great value if you're likely to want separates, even with shipping considered. For AV receivers etc, due to voltage differences you're better off importing from Hong Kong based stores than the US based ones, since the US runs on 110V not ~240V like us.
Finally, there's a a few quite good local (.au) forums for discussing this kind of thing, stereo.net.au, the home theatre section of whirlpool.net.au, and dtvforum.info