MEL - HKG try to get QF no matter how expensive.
((Look to see if HKG is doable with EK with a QF flight number via DXB), DXB to LHR might or might not be a QF flight number capable... not all EK flights can have a QF flight number, solely EK flights do not earn any QF SC, they must have a QF flight number, so a mixture of airlines, ie, HKG to LHR might be ok if you want, with CX, this is where a travel agent can do it better than us.
LHR to LAX then DFW then JFK will be with AA probably at a bit lower earn, and then the US back to MEL try to be QF flight number too.)
A travel agent might be able to get it a bit cheaper.
You probably have read too, that after Jan 16, any flights not with a QF flight number, will earn less SC.
Tried multicity on the QF website, it said to phone up QF telephone sales.
Some travel agents will give a slight discount if you pay in cash, rather than credit card.