One of the biggest frustrations I've had with the Pi is to be able to use it as karaoke machine. I have tried several methods but the guys from Pi-Fun seem to have discovered a way to make it work, but the method is somewhat complex...
The basic problem is to hear the microphone through the TV and play the .kar at the same time. The system failed but now has been updated the sound drivers on Raspbian and seems now it works.
The method requires two SSH connections and install a few packages. Fun is guaranteed.