One other thing (and this is NOT first-hand expertise). . . When I commented to a friend who has a fair bit of experience as a sound tech that I found the sound of a pennywhistle through a sound system to be a bit too shrill, he said that if there's an EQ on the soundboard, they should roll down the frequencies at around 1500 and at 3000 hertz and that would take out most of the shrill quality and give a more natural sound.

Just passing that on for what it may be worth . . .