A Burnett Salmon IS a Threadfin Salmon (though they're not a true salmon). Threadfin refers to the filament like fins just behind and below the gills. There are a couple of varieties of Threadfin, but the Burnett is the biggest. Some people also call them Kings.
I lived at Noosa for a few years and have caught them up at Lake Cootharaba. Live prawns near the reed beds.
Also get a few in the Mary River near Maryborough - fishing near creek mouths with big live river shrimps. The old timers used to say that when the mullberries started to ripen it was King season.
cheers,
steve