I assume this refers to the creation of CD media that are to be replayed on a car stereo system. In this case, the format to go for is simply a standard audio CD. It's the most compatible and versatile format. While many newer CD players probably do support the reading and replay of data discs with MP3 files on them, you cannot take this feature for granted. On some older CD players, you cannot even expect hassle-free detection and replay of any kind of home-made CD-R at all. Especially CD-RWs are problematic.

Not sure what Magix program you're using, but any Magix product that is capable of burning MP3 data discs can also burn standard audio CDs. Please keep in mind that WAV files are just another container file format that can, among other things, hold CD quality audio. A data disc with WAV files on it does *not* equal a proper ("red book" standard compliant) audio CD.

I hope this helps.