If you are just trying to play the music without vocal tracks then my Google search for "CD+G to MP3" resulted in at least one piece of software that would allow you to rip most karaoke tracks into regular MP3s that can be used via iTunes. I'm hesitant to mention or recommend it though as I know nothing about it. You will find it under that search phrase though.
If you are trying to keep the on screen lyrics intact then there are many programs to rip the CD+G format on your karaoke disks into MP3+G that can be used with several iPad/Pod/Phone karaoke Apps. (Note: It's the "+G" part that contains the graphical lyrics.) However, I do not know if these apps are compatible with air play.
Not completely unstumped, but it's a start.
With great power comes Awesome irresponsibility.