My system is hooked up to the OEM system via an Audiovox FM Modulator. I had planned to use that as a stopgap and put an amp in later, but haven't got a round tuit yet. Maybe you can find an aux-in adapter for yours? They do not make them for the stock Subaru stereos yet. Here is the thread I posted when I installed my stereo a few years ago, I have a lot of information in there.