I'm not so sure MB converted the files. There is no .asx file converter option in MB preference. The option to include one does not exist.
Sorry phred, but the Duplicates Manager does have the ability to convert extra files to the ASX format.
That's what the "replace with reference to the kept file" option does.
It creates an ASX file that links to the kept file, but keeps all the tags from the other file. So if you have a file that is same for a single, album and anthology box set, you only have to keep the one file to play, but the different info for the other versions are kept in the .asx file and used by MB when played.
@ kidjedi
Without knowing what settings you were using to filter your duplicates, its hard to know what went wrong. As you can see from the image i posted, MB is showing 2 versions of Sweet Dreams, but they are not really duplicates. If you could hover over the path you would see that one is a live version and the other is the original album version. These are only showing as I deliberately only used title to search for duplicates.
As for your original files before being converted to ASX, I think that MB does permanently delete them. Check one of those ASX files, and you may just have to edit the path to the kept file.