Hello, our Audi A4 Avant K8 would like to upgrade our Audi A4 Avant K8 with the 8 standard loudspeakers without subwoofers in the trunk. My plan; a little more bass must come! replace the front LS with FOCAL ES165K, what do I need exactly for it? (is a power amplifier needed or does it pack the original radio? an active subwoofer e.g. Axton XTB25 under the passenger seat, does not want to sacrifice the volume of the trunk. With the pictures of the Headunit, at the back left in the trunk, I can here the Loudspeaker Signal for On/Off for the Woofer turn off? Remote? The original radio has no chinch output. Thanks and greeting leugim