Bachmann EZ Mate couplers? Eeeeeeeeeewww. First thing I would do is take off those EZ Mate couplers and toss them in the garbage dump where they belong; they are droopy, are made of weak plastic and will often uncouple and "lift out" from an opposing coupler even when pulling a reasonable amount of weight. I would almost recommend the old-school "horn hook" couplers over the EZ Mates.
I'm telling you: Buy a pack of Kadee #5 and use the coupler box that comes in the package. Mount it onto the engine's frame with a drill tap and screw. That's my advice, but if you really, really, really must stay with the inferior EZ Mate couplers and Athearn's ill-designed coupler box, contact Athearn on their website at
http://www.athearn.com