According to this white paper (http://msdn.microsoft.com/en-us/library/windows/apps/dn466732.aspx), as of Windows 8.1, the AppX PlayReady Client can be used in desktop apps:
"AppX Frameworks are normally restricted to use by Windows Store app only. In Windows 8.1, the Microsoft PlayReady app package can be used by desktop or new experience desktop browsers."
Is there any sample code or guidance on how to actually achieve this using the media engine?