May be I will ask the flight attendant to check at door and give me back at door?

I think checked with original delivery box make sense as this is how Apple ship it to you after all. It should be good enough. I will add some cushion material inside like air filled plastic bag but it should be fine.

As long as you are on one PNR, the bag system applies all the way from US into China, so no worries on the quota, and CX will able to check though it to KA flight. You don't clear custom in Hong Kong but only in China.