So, this is weird and frustrating. Some of the files in that folder I can open on my windows laptop, and some still give me "invalid file type" even though it's .musx.
Oh weird, but using file > open, some of them just open, and some of them say "hey you made this with Finale 2014 so do you want the program to 'translate' it?" and if I click OK it just does. Wou...
Old computer: OS X, new computer, latest version of windows. The files are .musx files. Transferred them with a flash drive.
File was created in Finale, every channel's got its own instrument, nothing's muted or turned down in Studio View. I can insert staves and do as you say.