Here's how to handle sub issues:
1) Go get it replaced by the dealer.
2) Once fixed, here's the settings to use:
Bass Level: 0
Mid Level: between -1 and +1 to taste
Treble: to taste, but not over +2 in general
NF level: Just go with it.
3) Check amp settings:
Sensitivity should not be turn all the way up
LPF should be on
4) When the sub inexplicably blows again, repeat this process.
5) When you get tired of this process, write/phone/whatever MNAO regarding the situation and see if you can get money for a better set-up. I guarantee you can get a better setup for 150$ or less. (bramha, RE, or elemental designs low cost 10" subs, and some wood and carpet for a box...then run it off the same amp, at 4 ohms...just make sure the amp is facing the right way)