zenhigh

hey my aunt gave me a 92' sc300 for my birthday and i want to put a sub in the trunk. i know the car allready has an amp but idont know what its for. do you have to bypass it or can you go throught it to power the sub. ive been to 3 different speaker stores and got 3 different awnsers but they all say its a pain to wire is this true?so now im asking you guys. has anyonehere every put subs in my kind of car? if so tell me how you did it or how much it cost for instoling it