The YR and Airline fuel surcharges are both fuel surcharges charged by airlines. Try putting your LHR-LAX on an AA codeshare and HKG-SYD on CX. You basicaly want to avoid QF and BA code where possible.

SDEM is the Sudanese tax. It appears to be based on the cost of the fare. Given your fare appears to be pricing high, this should come down when priced correctly. It will still be several hundred dollars.

UK PSC is unavoidable if you stop in the UK. Given that you say you aren't, that should drop off when properly validated but double check that you haven't got a stop over 24 hours in there.

The Australian charges are the same. Best way to get those down is to eliminate a departure from Australia as they run about $80 a pop. HKG-AKL-SYD may work for you.