Shipping to Austalia would be about an extra $10. I'd have to pack it up and weigh it see if it goes past 5oz, in which case it jumps up $3.
I know that in Windows, you can only output to one sound device at the time. So the setup would be: the DAC to PC via usb, speakers to DAC via line out, and headphone to DAC via headphone out. It works pretty well as long as you have a separate on/off and volume control for your speakers.