You need to ask NAB specifically. Ask them if your margin covers shorting of equities.
The way margin loans work is the banks have a fixed security over the tangible asset. You are not permitted to buy ANY share, only selected and approved ones that you will be called upon to anti up if the margin is called.
It stops you from losing 100% of the facility without the blessing of the bank. A personal loan or line or credit is unsecured, and you can do with it what you will.
You are into hedging territory. Use the margin loan to hold equities (see if you can short), and use your personal funds to buy the currency.
The net change on your personal wealth is nil. Any gain will be a capital gain. Unless you want the tax deductability of the loan interest.
