One way or round trip?

If you ticket the CX flight as an AA codeshare, you can sign up for a Platinum challenge with AA and end the trip as AA Plat, OW sapphire, good until March 2017. Unfortunately AA doesn't let you use CX codes for the challenge.

If this is a regular route, also look at Oneworld's Circle Pacific product, $5K in J ex-HKG for a 22,000 mile ticket, $6100 for 26K miles. (HKG-JFK-SYD-HKG is just over 22K, HKG-ORD//JFK-LAX-BNE-HKG is under - you'd have to fly ORD-NYC separately.)