sound won't come out of headphone jack

[grantcahoon]

When I listen to my sibelius files, the sound will not come out of the headphone jack on my new Mac Mini. It does come out of the headphone jack when sibelius boots up and when I am listening to other music, but the sound only plays on the internal mac mini speaker (horrible sound) for anything I try to playback from sibelius. I just installed sibelius yesterday on my Mac Mini (rather - one of your technicians installed it for me). I bought a new Mac Mini but I've been using sibelius for 5 years on a Macbook Pro and never had this problems.

[MikeLyons]

I'm not a mac user, but on windows this issue is quite common. You have to look at the signal path to make sure both sibelius and the macos are directing the output to the right place.
Just because the audio file at the start is going to the right place is no guarantee that sibelius is sending its signals there. The startup music is just an audio file. Sibelius' output is a bit more complex.
Look at the audio engine options in playback devices to make sure the correct output device is selected. If necessary, go through the list one by one until you find the correct device. You might be advised to restart sibelius each time you change device to ensure the change is picked up.