Op is a dumbass and I call bs.
1. First the sub is blow. Than he says the amp is fried, with only a slight burnt coil, which is causing the amp to be fuked. Bro, get ur shit straight.
2. No shop would charge 400$ just to set the gains.
Sh it just doesn't add up, or he's jst fukin really dumb and ppl are taking him for $$.( which I would do too cuz this guy is a complete tool).