The 'standard' radio/CD player sounds better than anything I've heard in any of my other cars. Ever. Well, OK, I'm accustomed to old American iron with 35+ year-old radios which don't always actually function.
Seriously, I have heard, and, am accustomed to stereos/radios in modern cars, the 'regular' BMW radio is quite adequate. As far as listening environments go, an automobile is the last place to consider remotely possible any serious listening. C'mon, it's a car.