To play Vienna Instruments with Sibelius, you have to activate Vienna Ensemble. It then should be in the list of activated devices.
You can't play Vienna Instruments with Kontakt.
Andi
Vienna Symphonic Library
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When you click on the graphic keyboard in Vienna Ensemble, do you hear trumpet sounds?
If yes, please open the Sibelius mixer and choose Vienna Ensemble as output device for the trumpet. Also make sure, that it plays on the channel that you set in Vienna Ensemble.
Andi