Can't you just produce a listing at the file system level?
Code:
find /path/to/music -name '*.flac' > '/path/musicListing.txt'
or if you have multiple file formats
Code:
find /path/to/music -regextype posix-extended -regex '.*\.(flac|mp3|ogg)' > '/path/musicListing.txt'
I don't know if Synology will support this syntax though so you might need to look at the man pages, or just run the initial step multiple times e.g.
Code:
find /path/to/music -name '*.flac' > '/path/musicListing.txt'
find /path/to/music -name '*.mp3' >> '/path/musicListing.txt'
Notice the >> in the second line that tells it to append the results to the existing file.
Having said all that, surely there's got to be a better way of creating playlists.