SFO-HKG-DPS on CX in F or J is the best value out there. Do not add a feeder flight on AA since this will increase the miles you need disproportionately. You don't need to contact an agent for the HKG-DPS flight. It will automatically book in J. Try to book it on a day that they use a 747 though since they sometimes sell the F cabin for J.
Book as far ahead as you can (350 days) since multiple seats are few and far between. Enjoy DPS it is my favourite destination. Try to go between June and October for the best weather.
BA agents do not see more availability than you do on ba.com by the way. That is an urban myth. They can sometimes search partner bookings more efficiently.