Originally posted by Damek
That doesn't make sense. An "MP3 disc" is a data disc. So if you burn a data disc, it burns the music in its original format, and so if you have your music in AAC/MP4 format, it will burn a disc full of AAC/MP4 files. Unusable in a player that can't play AAC/MP4 files.
Or do you really mean that iTunes transcodes all of your AAC/MP4 music to MP3 format when you burn a data disc? That must take a long time...
No, that's not how it works. Say you want to burn a playlist of four MP3s and four AACs. Selecting the Data disc option will put all 8 on a CD (in their original formats). Choosing the MP3 CD will put the 4 MP3s on a CD and do nothing with the AACs.