System help

hey everyone...i made a huge mistake and went the cheap way of course..and bougth a 1400 watt pyle amp off ebay. i also used to home theater subs and now my system sounds real bad.(dont laugh) hah...anyways this guy at "Sounds incredible" in danbury ct didnt use a rca converter..and tapped into some wires in my rear amp in the trunk. (factory) is that alright or is doing that a big joke and makes it sound bad?..anyways i need some suggestions. I dont really have alot of money and im tryin to make this crap sound good. Anyone have any good ideas.? scrap the amp and subs..or get new subs, or what..i dont know what to do so hopefully everyone with sick trunk setups could help me out..thanks for your time

Jason