Thanks for the information guys. Just spoke to the agent, the booking reference for CX and MH are the same but I was told that I'm unable to log into CX's online flight management system. But yes, it seems the issue is with the booking class... I was told by the CX agent to give them a call 48 hours before departure in order to select a seat. It's going to be a 16-hour (!) long non-stop flight from JFK-HKG, I just hope I don't get an undesirable seat... On the bright side, I got this ticket for a very, very good deal, which made me choose to take MH this time.