I have a Toyota Yaris 2019 which comes with a factory amp. I'm trying to install subwoofers with the stock radio, and have very basic knowledge of the process. I found people use a line out converter to convert the higher voltage speaker wire signal to a lower voltage pre-amp signal. If there is an input into the amplifier for the rear speakers would I still need to use a line output converter? I found this youtube video of someone doing a similar job on a 2018 Yaris iA https://www.youtube.com/watch?v=GAlRuf2Q2Rk. In this video, he seems to connect his RCA cable directly into the amplifier input using an RCA splitter cable.