I think it defaults to a velocity around 60 so it sounds more realistic (I could be wrong) but you can edit the velocity of individual or groups of notes with Play - Live Playback - Transform (on Sib 7) it might be Play > Transform Live Playback on Sib 6.
You might find more info at the sibelius forum
Legacy Forum Post
about 8 years ago
Okay, thanks. All the insight is great. Please keep it coming!!! :D