5.1 Audio Speaker USB Adapter?

Hey guys,

I am from Australia, I just bought the Logitech X-530 5.1 speakers and I am running them off a Mac which I just remembered was two channel and only lets me play it out of one of three speaker sets. I am looking at getting an adapter, and what I have found so far is something like this:

http://www.smarthome.com/97374.html

EDIT: It says on that link in a few paragraphs down "Important Note: On a Mac operating system, the volume buttons of the adapter are not functional and there is 2-channel playback only." Does this mean if I buy one of these it still won't play through all six speakers?

And my question is will this actually work and let me play audio through all six speakers (including sub-woofer). Also, are there any other adapters or anything that are preferably available in Australia?

Thanks.