Slightly confused, the output jacks on the front of your CD DVD players etc will respond if your pop in a set of headphones, load up a cd with a song on it and, you should then hear ot playing provided that the volume slider on the front is turned up.
This will work whether you have connection at the back or not.
Try this first.
The output at the back is pretty well the same as the front but, you have a plugging facility to go into your MB.
Having tried this earphone thing, and if it works then come back.