Why not USA Australia return and nested Australia - HKG return ?
Ticket 1 LAX SYD
Ticket 2 SYD HKG
Ticket 2 HKG SYD
Ticket 1 SYD LAX
Or what ever city combination works
Or a USA HKG return with nested HKG-Aust return
Upgrades will be hard.
Or go visit a real walking talking travel agent (not a computer screen)
Oneworld has a circle pacific fare, but could be more $$ (AA QF CX JL) is not UA - Star Alliance