I have a $4K Audisson system. But it did not sound good until I stripped out the seats, carpets and all the interior panels and dramatically improved the soundproofing and sound dampening .
Because I listen to music more in the car than at home, it was worth it. But I might not of bothered if the OEM system had not sounded like crap (Mazda CX-5) in the first place.
You can get Dirac for cars. If I was starting over I would use JL Audio stuff (their subs are amazingly good) plus this:
https://www.minidsp.com/products/car-audio-dsp/cdsp-8x12-dl