I already said I downloaded the manual for the PTA1000.
Those specs it lists aren't worth being written on toilet paper. The final "total power 1000 watts" is meaningless.
Is the 250 at 8ohm based on one channel at a time? Both channels? 1kz? 20-20K? Continuous? What it managed to choke out before catching on fire?
You probably need to check the wiring inside. I would wire that, with this amp, in series...since you are bridging it. That presents an 8ohm load which this amp "delivers" 500 watts.
What frequency is the port tuned for? 30hz? 35hz? 40hz?
Is the box braced in any way? Does it have any poly-fill?
Have you tried stuffing the port with some dense foam?