i'm starting to wonder if the box caused the cone to "stall" at some frequency and that led to overheating the coil. that makes the most sense. i will run some more tests to verify and change the box design if necessary. i dislike the port placement as-is anyway.
thanks for the responses everyone. I think we kept this thread from getting out of hand, a rarity in this day and age. Good job not acting like e-thugs!!!