My goodness, me too! I am fixing a large gin & tonic!

I was reading the entire thread and conversation and hesitated to post my $0.02 as there were enough people posting advice that I would have given anyway. I was on the verge of contacting OP today if there was again no positive outcome from his/her effort today, I do know someone quite senior at AEXP Travel and would have asked him for a personal favor to look into it for OP and try and fix the issue as it was clearly an egregious instance of apathy, incompetence, BS, laziness and dumb luck that OP got shafted with this problem. I have had issues rarely with AEXP but am particularly harsh and merciless with them on the phone if they give me the runaround, it also doesn't help them that I know how bookings work and what they are able to do and what they are not.
AEXP clearly had the ability to resolve the issue but they chose not to, because someone on their side goofed up badly and cancelled the JL005 flight which put everything into a spiral when they should not have. JAL would have had the ability to take over the reservation and make changes but AEXP probably prevented them from doing so, hence they kept pushing back to AEXP.

Honestly, I am fed up with current state of affairs with travel support with agents as well as with some airlines. They hire incapable people who are not able to think outside the box, don't understand what you're trying to do, or too lazy to try harder to resolve your issue. What I have found is that supervisors at airlines can literally do whatever they need to in situations like this, and it's art to be able to connect to a supervisor. The other issue is codehares, once you have a problem with a flight or airline, I can guarantee they will mess you about and kick you back and forth to each other saying its the other airlines responsibility and not theirs. So, as much as possible, for personal bookings, I prefer to directly book with the airline, that way they are directly and solely responsible for fixing issues, and also I try and avoid codeshares, too much scope to shirk for being left in the cold if something goes wrong.

What does help is doing research and this is where forums like this and all the knowledge advice you get from experienced users is helpful. Also, patience, creativity, being logical and reasonable and being to the point with the other party. Being armed with information helps, as this way you can guide them (I am a full subscriber to ExpertFlyer), and also find call centers in other countries where the wait times will be less (like Australia, or in Europe etc.). I also feel that sometimes if the agent doesn't like you, they note it in the reservation remarks section and as a result other agents give you the same runaround, but maybe it's my imagination.

Anyway, glad you got it solved, not the most ideal situation given that you have to go through DFW, but better than the other alternative you were facing!