The move towards B&O audio is less about sound quality for the german and swedish automakers, more about marketing and investment. Many stereo companies make car specific audio systems and then "sell" them to the auto makers to get their names on the sales and marketing collateral and in the car itself. They have frequently found on high end luxury cars this leads to those same buyers having brand loyalty when they outfit their home.
However, BOSE, HK and many others have given up on this trend and instead have focused on being in the mid-market vehicles and selling their ear buds and headphones, wireless speaker setups, etc. This is actually a higher volume play for them and proven to be more profitable. B&O doesnt care about volume, they want exclusivity only.