The problems are BKK-HKT is not on CX/KA and the time of travel is around Christmas. Fares will be high.

I live in SFO. If I fly to Asia, I normally fly HKG and then add CX/KA segments. That is a lot less expensive. I normally do it with a TA, as my itinerary is too complicated for CX.com to handle.

Also BKK-HKG-HKT can be less expensive, but the travelling hours will be very inflexible.