I just got my 2019 Nissan Altima SR non-Bose system installed and am having some strange distortion on 3/4 volume and a tough time tuning. If I do tuning myself with processing defeated it sounds better overall tonally but lack the time alignment, at that point it is just crossovers and EQ. See my setup below and recommend my next course of action. Be it active 2 way in the front using my existing speakers, 3 way with a midrange from the same series, make a center using an aftermarket enclosure and 6.5" coaxial, change DSP, or settle with what I have gotten. I have tried the measurements several times with level matching and various volumes but still am getting the same issues. Tweeters in factory dash locations, woofers in the front door, 6x9's in rear deck. Sub in the trunk facing outward.

My System:

JBL GX608C 2 way 6.5" Component - Passively crossed over fed from Channels 1&2 of Kenwood Excelon X301.4
JBL GX 3 way 6x9 Coaxials - Channels 3&4 of Kenwood Excelon X301.4

Diamond Audio 12" Sub inside of OBcon Godzilla Slotted Enclosure. Single Channel of Kenwood Excelon X500.1