Here's a link to modifiedlife's Durango page showing the wire colors.
If you are adding a LOC for an amp to drive a sub, you are probably better off using the rear speaker wires, the last four wires shown on the listing. If you are adding an amp to drive all 4 channels, then of course, you need to convert both fronts and rears. The simple method is to tap directly into the appropriate wires and connect them to the line converter. If you do not want to tap the wires, you can purchase aftermarket wiring harnesses that are made to plug directly into your vehicle radio and/or the vehicle wiring harness. The Metra part number for a stock radio harness is 71-6502. It plugs into the radio and provides pigtail connections for power and speakers. There is, of course, a harness that plugs into the vehicle harness itself, allowing you to make the connections without any cutting or tapping of the original wiring.
Hope this helps.