The reason for not just automatically attaching every mp3 in a directory to a single PDF, because if there are multiple PDFs in the directory (which is the case for most users performing a batch import), it would incorrectly add all of the audio files to every song created from any of those PDFs. That just isn't the right behavior for most situations. I also don't believe most users attach multiple audio files to a single song (some users certainly do, but I don't believe it's the majority). I would have to add a new setting that controls whether MobileSheets tries to account for situations like this where there are multiple audio files with file names that start with the same name as the PDF, but have different suffixes, so that they can all be added to the single song that is created. Without that, there is no easy way to do what you are trying to do right now. The best thing to do is just to ensure every song has a unique title and filename across libraries, then you can export to .msf and import the .msf without any conflict, but I recognize that this may not be doable with your scenario.
Mike
Mike