What do audiophiles do in their cars?

I listen to SiriusXM, CDs, FM in the AMG (Harmon/Kardon).  Best sound of my vehicles.

CDs and FM in the Z4M (Bose)...same as in the 97 Ford pickup truck.  Just replaced the truck's 4 speakers with Polk 6x9s, uses the original factory head unit am/fm/cassette with a 6 banger CD.

Just to keep it real...1976...had an am radio in a 69 Skylark, added the cursory (and terrible) FM tuner, 8 track player and rear deck speakers.  Accidently discovered the 8 track owner's manual last week... still have it after 45 years...don't ask me why; and looking back whoever thought 8 track was a good idea???  Sign of the times back then.

2018 Tundra Crewmax...Alpine head, Morel Ultra speakers (component in the front and coax in the rear), 2 AD 10" short throw subs in a custom box behind rear seats, Morel 4 channel amp for the speakers and mono amp for the subs. And then lots and lots of Dynamat extreme. 
I use my Samsung S21+ wired to the Alpine via USB C and running Andriod Auto. I play from Amazon Music HD to give the highest fidelity as the source. 
Basically, it gives fairly clean and clear music at most volumes I want to play it at. Even when I am not playing music, the sound dampening means the cabin is more quiet than most vehicles short of high end ones. 

If there were a less expensive quiet reliable car I’m all ears. Not yet willing to switch to all electric cars because of the inconvenience of finding the limited charging stations vs gas. Seems luxury cars only ones available. Got my $85k car for $45k used - someone else ate the depreciation. Not used to expensive gas and expensive maintenance and the car is rather large for my needs.

The quality of the stereo system never impacts my car buying decision because nothing that is OEM (including upgrade options like Mark Levinson, B&O, etc.) is worth the price you pay. Even the renowned Lexus Mark Levinson upgrade is very poor sound quality. The speakers seem like they're made of cardboard. So I buy whatever car I like and then custom build my audio system. I do it because I drive longer distances and the music helps me relax. If your ear is "trained" to hear/notice differences in home audio setups you will also hear them in your car. I usually drive with the windows up to minimize outside interference. If I feel like a nice breeze of course the sound quality suffers but the option is mine. If you don't know whether it's worth it just go to a custom sound shop and listen to one of their demo cars while driving. 

In my collector cars I don't have music, I enjoy the car.
In my everyday cars I listen to BBC Radio 4, the best radio channel in the world, and CDs on long overseas trips where R4 is difficult to pick up; I also talk to the wife.

Sooliwen Congratulations on your first post, and welcome. You are absolutely correct about overpriced car upgrades.  This is where the manufacturers make all their profit.  If you buy used, even after just a year or two there is no premium for the fully loaded versions - if that's what you want, that's the way to buy it.

There are still some enthusiasts who compile home brewed lashups with huge amps and speakers in the boot (trunk).  This was very popular in the UK in the 70s and 80s.