Just wanted to share my experience on improving audio in my 2017 Mazda 6 touring non-bose. I added Kenwood KSC-SW11 utilizing the PAC AOEM-MAZ2 which was a very easy plug and play install. The sub fits perfect under the passenger seat. Not the cleanest bass but did make a improvement of lows, and I would recommend. I switched out rear speaker for Hertz Hertz Audio DCX 165.3 6.5” to improve the highs in the rear. I also added sound dampening to interior and exterior of all door. The sound dampening definitely improved the sound quality of the stock speakers. The one component that I think made the biggest improvement in sound quality and I would definitely recommend would be adding 3.5” mids to the dash in the existing cut outs. In my case I simply used the existing twitter wire and connected it to a pair of Hertz DCX 87.3 with an inline bass blocker. I utilized a 3Pin PC Fan Power Extension Cable to tap into the exiting harness as it fits nicely.All in all I did not want to break the bank as I spent around $300, of which made a noticeable improvement. Below is a video I found for dash mid install ().