I can't help you with DisplayConfigX as I don't use it, but for the sound issue you need to provide us a lot more information before we can help.
How is the audio system and Mini all wired up?
Do you get sound if nothing is connected to the audio port on the Mini?
With headphones?
If you connect an iPod/some other audio device up instead of the Mini, does it work?
What about playing from iTunes or system sounds?
Not to be too obvious, but you don't have it muted do you?
-dave