Are you sure that EK has not just done the equivalent of "dynamic currency conversion" which is usually worse than your credit card FX fee? Fares are constructed using IATA's internal currency, NUC, which would then be converted to the commencement country's local currency (AUD) via the rate of exchange specified in your fare calculation on your e-ticket pdf - those fares are then propagated via the fare distribution systems. I think it would be strange for EK to break protocol that way by issuing a ticket ex-SYD in GBP directly...