http://www.nch.com.au/switch/kb/1405.html
Quoted from file-extension.org:
The XKR file extension is associated with the Sing Magic a karaoke on-line service, karaoke song format and karaoke song player for Microsoft Windows. The *.xkr file stores karaoke song playable in the Sing Magic karaoke player.
This file type is not meant to be opened directly, there is no software that could open and work with it directly, or there is no information available in public sources about opening this file type. This is usually the case of some internal data files, caches, temporary files etc.
As far as we know, this .xkr file type can't be converted to any other file format. This is usually the case of system, configuration, temporary, or data files containing data exclusive to only one software and used for its own purposes. Also some proprietary or closed file formats cannot be converted to more common file types in order to protect the intellectual property of the developer, which is for example the case of some DRM-protected multimedia files.