krazyknuk

you will need the processor. There are no speaker level inputs on that amp only outputs and RCA inputs. LC2i is a good choice if your only adding subs

The factory sub will have speaker wire going to it like all speakers do. Sometimes it will be a manufactures default clip style plug in. You can simply cut it off and use the positive and negative to connect to your aftermarket sub. There should be an adapter you can purchase if you do not want to cut it off this will be easier to reinstall the factory sub later. Also I would have a look at the amount of power your other sub/subs require. Typically factory installed subs don't take a whole lot of power and you may be disappointed in the sound quality or worse the impedance won't match up and you could kill either your factory amp or your subs. best thing to do would be add in a new more powerful amp that will work well with your new subs

The easy way is to just replace the speakers and use the amp that is already in the car. Just replacing the speakers will generally improve the sound quality. Having said that a new amp will make it sound much better than using the factory amp. You don't have to replace the head unit "Sync" to install an aftermarket amp you will however need a line converter to do the job. A line converter connects to your speaker wires and converts them into an RCA audio signal so you can install an aftermarket amp. If this is all Greek to you best to take it to a good car audio shop and get it done. to give you a rough idea you should spend roughly 200-400 on a good line converter.....just get a good one (audio control or Audison are my favorites). Amp should run 2-400 as well. Install and parts for installa good shop will normally charge 3-400 for the install. Also you can just install the new speakers and see if your happy with that if you want more then try option 2 Good luck