If your factory amp and speakers are ok ( its highly likely they are ) your new Kenwood KMR-M318BT should sound Fabulous .
You do need the the Kenwoods speaker outputs to be the input to the factory amp the correct way .
Get a pair of Audiophile grade Mundorf capacitors ,MU-ECAP-270U-63V-BR63 ( aka 6db bass blockers) put on your door speakers ,then All will be Well in Crossfire Musicland :-) i promise.
Ps ,i bought mine here :
https://www.soundlabsgroup.com.au/p/...olar+Audio+Cap
Enjoy The Music, ( without spending much)