Are you comfortable removing the stereo? Running power/speaker wire? Understand how everything is connected? (ie- red/black/blue wires? high/low level inputs?)
There are 2 basic ways to connect an aftermarket sub system to the stock Infinity system. There is an adapter to run RCA out of the stock head unit/amp. (I think it's a Mitah brand adapter, you can probably search for a link) You can also connect a high to low level converter off of the speakers. This is the traditional way to hook up an amp to a stock system. Some amp may have high-level inputs, do you have an amp yet?
nah. don't have an amp. i wanted to research all this stuff to make sure it was possible to hook up amp/sub. i have subs and in shop at school the teacher is ordering wood for sub boxes so im gunna be making a custom enclosure and everything. i just wanted to figure out how hard it will be. i just finished puttin neon in the car and i've been learnin a little bit about wiring shit up so i figure now's a good time to start learning how to wire up subs/amp so im ready when the time comes.