There's a website called Discogs that's kind of like an ebay for music, but it's also a database that tells you all about different physical releases of music in surprisingly good detail. If you search for "CX5M," more comes up than you might expect. One album in particular, "The NDO Takes Off!" by The New Digital Orchestra caught my eye. it had this note on the page:
The digital music data on track 14 (for the YAMAHA CX5M Music Computer) should be saved to cassette tape for loading purposes. (Consult the CX5M owner's manual for instructions on loading music data into the Music Composer software program). The manufacturers assume no responsibility for loss of data for any reason, and suggest saving data to tape when the album is first played, using a fresh stylus, and ensuring that turntable speed is accurately adjusted.
Sadly there were no recordings online. I told a friend of mine who rips vinyl on youtube about it and the next day he had bought a copy and recorded the whole thing that you can listen to here. I never quite got the hang of loading data via the cassette port but I did load the data track into openMSX and it had YRM-101 FM Music Composer files for three of the songs on it. B1-3 on the playlist is recordings of those, and D1-3 are the data files (with Stop In The Name of Love as a stopgap for the sake of your eardrums). Figured some of you might get a kick out of this :)
Thanks for this!