Your Playback Configuration looks good. (Since you're on Mac, you want to use the AU version of Kontakt anyway, not the VST.) Well, the Sibelius Player sound set doesn't look right. When testing/working with the following, remove Sibelius Player and just have VDL in the configuration.
1) Can you manually trigger sounds in Kontakt Player when in stand-alone mode? If yes....
2) Do the TriggerTest files playback as expected?
3) What's the exact version of Sibelius?