If you do a dummy booking at aa.com for a SFO-HKG-BKK roundtrip booked as AA codeshares it will show you the AAdvantage earning when you click through. I just did this, AA awards 15,958 EQM...6 more miles than GCM.

In discount economy, this should theoretically match the base miles for booking the CX flight numbers.

Unless this flight was in late December where there would be little chance to fly more, I would just book it as-is and see what it credits before spending more $$ on another trip or to add segments, etc.