I did this once in the reverse direction (HKG-NRT-DFW) and CX arrived at the gate adjacent to the AA flight. There was an AA agent on the jetway with a sign for me and took me over to the other gate (it was a close connection and they had already boarded). Without the agent I suspect it is a rather long walk to the main terminal, and then back to the gate area which is in a satellite concourse. You won't have to go through japanese immigration and customs if you are transiting.