What I will add to this conversation is that I was surprised how my car stereo uses less DSP manipulation than I originally thought I would need.
I use the Dayton DSP-408 which is likely all most folks will ever need in a car.
I get the most out of it's active crossovers and the PEQ. These are indispensable. Time alignment and those kind of goodies are really of zero help for me due to the fact that my stereo is designed to sound equally good to both front passengers.
I never want my GF to have second class sound.*
*You can save several presents so one can build a fully time aligned system for the driver and then switch to a preset with different parameters when another person is in the front passenger seat. I did not set up a driver only preset but I do have presents for windows up and down, stuff like that.
What gave my car the sound I wanted most was moving the subwoofer up front, putting the front stage on the dash, using high order slopes, and using zero rear fill.
Then next using PEQ to adjust the response. (wow does this get tricky in car, so use a moving mic method to gather frequency data - a stationary mic is worthless)
The only time alignment is to add some delay to sub.
Everything sounds like it playing on my dashboard like with a pair of stereo home speakers, there is no sense of sounds coming from either mid-bass nor the sub.
On the dash are 3/4" tweeters & 3" drivers (playing 380hrz up), in the doors 6.5" mids (120-380hrz) and in between the front seats an 8" woofer. (120hrz down - doesn't really hit much below 30hrz but oh well)