I only heard these birds, and failed to see them.
But I am very familiar with the calls of the Yellow-tailed Black Cockatoos and I know what I heard was definitely not Yellow-tails.
The calls I heard were similar in tone and wheeziness to this recording:
Time of the hearing, was approx 4:00PM, January 17, 2013.
I am aware that they are recorded from Kangaroo Valley, where there are suitable stands of "Black Sheoak" Allocasuarina littoralis (along the Bendeela Pondage road - personal sighting).
I have previously reported seeing this rare Black Cockatoo species from the Wollondilly Valley and Nattai Gorge area, off the Wombeyan Caves Road, west from Mittagong. In that case they were feeding on the longer-leaved Casuarina glauca (I think that's the correct species name.)