So you save money on FX transfers to buy US listed shares, you get an AUD wallet which gives you access to wholesale FX rates from OFX.
Macquarie Bank powers these wallets by providing you with a Cash Management Account in your name, has it's own BSB and Account Number for you to deposit funds in whenever you like. We have gone down this path as the FX commissions provided by Australian banks to make international transfer are too high. We negotiated a rate with OFX that will apply to our customers and allows them to access this rate directly from their AUD wallet.
More information on the AUD wallet (CMA) is provided in these FAQs.