What i did with my system is my 4 channel amp in under the floor of the trunk and i ran 4 sets of speaker wire to the back of the deck then reused the stock lines. I have been using the stock lines with 100 rms per channel 4 channel amp for 6+ years never had a problem. What you can also do is run speaker leads directly to the rear channels then use the stock rear speaker leads for the front doors. So what you do is run 2 sets of leads off your amp the the rear speakers one set goes to the new speaker another set goes to the factory rear lines. When you have the new set hooked up to the factory rear lines you go to the back of the deck then cross the rear lines with the fronts turning the factory rear speaker leads to front speaker leads. This way saves you a lot of time from running speaker leads to the back of the deck or thru the doors.