I think I figured out how to get a #MIXXX playlist created on my desktop to work on my Surface:
1.) create the playlist with the library on a external drive
2.) export the playlist with relative paths to that drive
3.) export the playlist with relative paths to that drive AGAIN and replace the existing file
4.) open the playlist with a text editor and replace the desktop username with the surface username (only for special character absolute file paths)

Improvement suggestions appreciated...