Pretty positive you have to replace the RCAs, remote and all that fun. I did it in my 04 spec. If you have the stock HU you also have to get a LOC. See the replacing Sub and Amp bible
Here
The best how to info is towards the end...SR20Demon went through it step by step with me.
Also...FYI you can't get rid of the stock amp because it powers your rear speakers.