[Wayne]

If you're using standard CDDA tracks, you won't use MP3 files anyway, therefore "kbps" of the track is irrelevant. Your MP3 files will have to be converted to WAV files first, then they'll need to be up or downsampled to fit the criteria I listed above for CDDA files, then you can inject them into the image (or burn them using the Echelon tutorial).

As to not being able to fit all of them onto the disc, you will need to edit the WAV files to shorten them so they'll be about the same sizes as the original files. You can load the originals into a WAV editor and get their actual playback time, then just shorten the new songs so they have the same playback time. Depending on the editor software you're using, you can even clip the ends off the songs and FADE the remaining music so it sounds like a natural ending. Editing audio is somewhat of an art, so you may find it challenging to make it sound just right, but it can be done... For instance, about 10 years ago I took a .VOC file of a sound-snip of "Spock" saying "...the good of the many outweighs the good of the few". I changed it so it sounded like he said "...the good of the few outweighs the good of the many". This edit was particularly difficult because I didn't have any hightech editors (like CoolEdit), but rather a simple (ancient) VOC editor that came with my first Soundblaster card. None the less, it sounded quite believable.