You can either purchase and amp that has high level inputs as well as low level inputs. The high level inputs will take 2 channels from your factory deck and use them as a signal source rather then rca's. The low level inputs are simply rca's incase you want a future upgrade. Also, there are converters out there, Ramos or someone else can tell you the name probably it escapes me right now but it will take two channels from your deck and convert them to an rca line which you can then simply pop a set of rca's into your deck and your amp. That would be my preffered method of the two they you can continue on with any amp you like, not all have high level outputs.