Hello. Do you have the 2-way system? Or the harmann kardon?
If you have the "normal" 2-way system, you must leave the output on the pioneer set to 4-channel. If you have the HK, you will need an adapter to feed the factory power amplifier anyway, and if you want to achieve the very best result, you can also use the pioneer to feed the front system directly activ. With runtime correction, high-pass filter, phase control and everything your heart desires. However, all 4 speakers (2 tweeters & 2 mid-range speakers) must be connected to the radio with one cable. Top radio!