I think you've been getting some real crappy advice.
First of all, f*ck all this ghetto porting and all this bullsh*t... You have a really high excursion sub that should be able to reach pretty high volumes in a sealed box especially with that amount of power.
With that said, switch the 4 guage from Nine.2 and put it in the Nine.1 instead. I can't believe no one told you to that yet!
Next, set your lowpass lower, probably down to 60 hz or something around there, play around with what sound better.
After that, get a multimeter, read the gain setting tutorial and set them properly!
If you still have problems after that, I will have to say that someone ****ed up the wiring with your Nine.2 or something like that especially if it affected your other sub somehow.