I've never found the environment of a car good enough to worry about my hi-rez flac files being played in my car (2014 BMW-328 which is fairly quiet). I use XLD to convert all my files to a format that can be played by the car on a USB drive. I needed a consistent format for my car and my wife's 2016 forrester. I chose 320 kb AAC. XLD does all the necessary file conversions. (My BMW will play flac, but my wife's subaru won't) I can also play off our phones, but like the USB drive permanently plugged in as the best solution. I have two 64 GB usb drives I bought on sale for like 12 bucks for both of them. I can store almost everything I'd ever want to listen to out of our vast CD and high rez flac collection in that format, so I basically have all my music in the car. One caveat is I have to rip the CD layer of SACD to have those files available in the car.
For the most part, I listen to XM radio, and use the USB drive rarely.
Supercharged Song Towers, Oppo BDP-203, Anthem MRX-520, LG B6 OLED
Headphone Rig: Oppo BDP-95, Burson Audio Soloist MKII Headphone amp/ Sennheiser HD800S, Sennheiser HD650