What do audiophiles do in their cars?

At least a bi-amped system with electronic crossover. I have an older Sansui preamp with cassette and added CD changer and now digital inputs.

Most higher end, esp European, cars have such extensive sound deadening and even tuning that greatly diminishes ambient noise - some even have white noise generators built in (e g. Bentley). Somehow they also tune it so you can hear the motor (esp high performance motors). My M-B  M500 and, even moreso my VW Touareg, are extremely quiet, even at 90mph down the road, with doors closed and windows up. Which makes matching and the tuning the audio systems easier for the manufacturer. I had "audio package" on the Merc that was like a $2800 option package (! I bought it used) that specifically mentioned more sound deadening and tuning and 400W amp, separate preamp etc. Harmon-Kardon was the supplier. And it's a specific system designed specifically for that model (doubtless from a pool of common components across models, manufacturers, price points). 

I usually change out the speakers. Most factory ones are cheap paper crap. Add some dynomat to the doors. Helps reduce road noise as well. Sometimes add a small sub. I like focal’s in a car. Running Infinity Kappas now. 

Listen to AM radio..I'm done tossing money away on car audio...I did when I was young and foolish.