As you know the yi d aki is a one-note instrument. The creativity of the player comes from how well he controls these elements. What was learned at Garma was just an introduction of these elements. This rr sound showed up in many of the mnemonics used during the class. By i.e Gumatj Of these the rr sound as used in mnemonics seem to be a be big factor in getting that N.E. Arnhem Land sound.
Stress is always on the first syllable.
Most of this information was taken from handouts received from Michael Christie, and Mike. As I understand it, you can coach quite different sounds out of a yirdaki by giving it a turn and then playing it in a new position. All my Djalus have nearly perfect mouthpieces without beeswax on them. I've heard of this too. At Garma I observed many Yolngu players turning the yirdaki they were about to play.