that's where multiple file choice comes from:
let's say that you have a file called: A0000001, A0000002, A0000003, A0000004.
If you put '6' at # of files, and type A0000001, A0000002, A0000001, A0000003, A0000004, A0000004, MuseInc will export the music in that order.
It makes making music quite easier.