Garmin Map Card + MP3 Files?

BMW Nav VI. I currently have a data card in the Nav VI and use it to play MP3 files and always try to load routes and such to the card instead of the internal memory. I’m looking at purchasing a Garmin map card for South America and wondering if anyone has had any luck loading MP3 files onto a Garmin map card, since it replaces any data card already in use?

I guess my other option is to purchase a download version of the SA maps and download to my existing data card, but I’m not sure if that will work and besides, I might have a chance at passing along a data card at the end of my trip—and that can’t be done with the downloaded version.

Anyone been down this path before??

Thanks,
DeVern