OK. So if I book through a TA, that TA will have to contact one of the airlines (which is AA, CX, or QF for my case) to verify the routing and receive instructions from one of the three carriers on how to book/ticket the whole thing? I'm not sure how the procedure goes when a TA is involved since there is no OW hotline for the TA to call should they have questions.

The reason why I am seriously considering a TA is because I called CX and they said they do not accept debit cards to make payments for such bookings. I cannot use my credit card because the fare will most likely exceed my credit limit on the card. Booking through the TA, I can pay with debit, check, or even cash. I guess I just have to make sure the TA issues the ticket under CX stock.

As for the upgrade, I can directly contact Asia Miles for that as long as I have a confirmed revenue booking regardless through CX or the TA I assume. All I have to make sure is there is an award space for the flight/date (Z class in this case).