Comment 5 for bug 315405

I agree
1. that this feature would be a welcome addition to Sound Juicer and
2. that it is frustrating that this bug simply expired ...

... however, it is probably not a high priority feature to incorporate because a command line workaround is rather simple:

$ ls
Disc 1 - 10 - Centerfold.mp3 Disc 2 - 20 - Up Rock.mp3
Disc 1 - 9 - Walking on Sunshine.mp3 Disc 3 - 1 - Never Ending Story.mp3
Disc 2 - 1 - Scatman.mp3
$ rename 's/^Disc (\d+) - (\d+) - /sprintf("%1d%02d-",$1,$2)/e' Disc*
$ ls
109-Walking on Sunshine.mp3 201-Scatman.mp3 301-Never Ending Story.mp3
110-Centerfold.mp3 220-Up Rock.mp3
$

For more options read:
$ man rename
$ perldoc perlop

This workaround added to launchpad so that others don't need to reinvent it.

enjoy!