I was helping someone yesterday with a similar problem. They wanted Gox USD and had local currency. Easiest was for them to buy coin and transfer direct to the exchange. Even with different currencies on different exchanges, it is hard to move it around - coins are easy. It would be similar for AUD trades (I have a ComBank account I use when I'm in Aus). Fastest is an OTC among a group that has built mutual trust - like ebay perhaps - and I have several people I trade with like that.
For example, if you want AUD100 in TH, then easiest is buy by local internet transfer and receive coins and I can execute the trade directly in the exchange to cover the position. Having a market maker helps, or realising you pay for the speed and ease. For instance, last time I move some money around took six days from my bank to LR (including a weekend) and then between 10 minutes and a few hours into the different exchanges. Somewhere along the way I lost 3% to 5% in conversion fees because of forex spreads and handling charges. At least trading directly I can use mid-rates.
Similarly, if you wanted AUD for BTC, having someone happy to buy the coin direct and transfer is handy, but it doesn't work if they're trying to make a business of it, then the fees kick in.