Well, I only use APL files because there's no way for MC to save tag data to a CUE file. And I don't trust my library enough to only keep the data there. What if someday I decide MC's no longer for me and I want to move on? Not that I see that happening in the near future
mpl ? mpl does not care what format your media is and it saves everything MC knows about it.
If you decide to move on, you would need an app that could import xml, you make xsl and that should be it.
I'm moving towards a system that only keeps data in the library and a mpl file per album. Just wish it was quicker to save to mpl, there are currently quite a few steps to do to get save to mpl to happen. Wish there was a way to automate it, so it was just a button on the toolbar.
This was after reading your post some time back about a hard drive going bad slowly (worse than losing it outright, now you have dirty data but no clue where it is),
..the only way to protect against that is checksums.