Hi David
Are you sure your car is capable of playing flac files? Assuming of course that your B2 is set to compress to flac.
If the car is mp3 only there are a number of programs available which will convert your flac files to mp3 using a PC..
You will have to keep your back-up disc as it is for use only as a Brennan back-up and put the mp3s on to another disc to play in the car.
Brian