non-Mac drives need a different standard.
if you use Toast6, you can choose "mac only" "Mac & PC" and "Iso 9660" - a mac can read all these file standards, PC and car stereos not ;-o
I choose the iso standard and my dvd player reads mp3CDrom fine.
no idea, about dvd-r.
no idea about car dvds (you make me jealous!!)
you did use the "internal software" of Apple?