Hmmm a 1 week rush job that ended up damaging your equipment. Sounds like you have a case against these fuxors. A professional install should most definately include gain settings as thats a very critical part of any system. Why would they put a gain control on an amp if its not important, it directly effects how much power the amp puts out and is used so you don't blow anything.
I personally would've thrown a brick followed by a molotov through the front window after he tried blaming it on me.
Anyways I hope it turns out for the best, and just so you know I learned how to install my system in about 2 weeks and went from knowing very little to a lot. So its not that hard to do yourself next time and you know its done right plus all that hard earned money you get to not donate to some prick that takes advantage of his customers.