I agree with nen that A/B is the way with acacia. I've had some good luck with acacia's both bark and phylodes. Never with A. acuminata though as it aint to be found in my neck of the woods.

Definitley go the A/B on the phylodes and and any twigs. A friend is going to do an extract on some branch wood from another apecies soon as we were lucky to come accross some downed material. I have not heard too much about branch wood but twigs and phylodes are a definite especially with acuminata i hear.

Taking bark from live trees even if it is a small amount can do harm. Pruning some branch material can usually be done safely with most species and i have successfully done this with A. floribunda.