As far as I know, and I have done limited research, Henninges held a responsible position under CTR and was sent here to Melbourne to get things going in Oz. Henninges effectively created the first major split in 1909 (the report in the WT for that year reflecting this, although not directly reporting it.)
I have seen Henninges' grave here, and his wife Rose (of some fame herself), who died later, is buried with him. Their grave is in need of some repair. From memory her name appears at the National Australian Archives web site.
Henninges' group still meets and I regularly receive a copy of their public material. They have kindly provided me with a little information on Henninges.
Cabasilas, maybe if you write to them, they could be able to advise you of the books or other material they are able to make available to you.
The Melboourne State Library holds a number of his books, some of which are in German.