The CD plugin should be enabled by default. You shouldn't use the "Open Exaile Music Player" option available in the CD directory in the file manager. What you need to do is start Exaile normaly (for example, from the start menu), then in Exaile go to the tab labeled "Audio Disc", which is on the left by default. From there you add tracks to the playlist so you can listen to them.
The "Audio Disc" tab may not be available. For example, when I start Exaile for the first time it's not available. When I restart the Exaile once or several times, then it becomes available. Exaile just seems buggy. I don't use usually. Make sure Exaile is closed, if you try to restart it. Closing it from the window's "X" button will just hide, and be avaible only from the tray.
