That's a relatively ambiguous question. How does the Sibelius volume compare to your normal system audio and playback in iTunes?
One thing that will give you a bit more juice can be found by going to your instance of Kontakt Player 2 in which you have VDL loaded (can be accessed via the mixer or Playback Devices). Then click on the Options tab and set the default loading volume to 0db instead of -6db. I think it should be doing this by default, but I'm not sure.
See attached image.
Legacy Forum Post
about 12 years ago
If you haven't already, I'd suggest updating your VDL library to version 2.5.2. It has a better volume presence than the 2.5 library out of the box.