Kingianums occur naturally as far south as the Hunter Valley, which isn’t that far from where you live, so they must be able to tolerate cold temperatures.
If they are hybrids then the thing they are most likely to be hybridised with is D. speciosum, which has many forms but some at least occur in Victoria, so again very cold tolerant.
I grew a few straight kingianums outdoors year-round in Patonga (sthrn Central Coast) and made no special provision for them in winter. They thrived. Cold place in winter, Patonga. Also in Epping (temps down to 2 degrees) and they thrived there too.
If they were mine, I’d leave them outside most of the year, but bring them inside to an unheated room in the coldest two winter months while seedlings, but not as mature plants.
In terms of their preferred winter treatment, just think of the winter conditions around Coffs or Port Macquarie, the centre of their distribution. Winter is basically like summer, only colder. Not particularly wet or dry.
Of course if they are hybridised with something else then I have no idea.
Apologies if I’m stating the obvious here, but a handy thing to do is to look at this map of BOM stations and see which one you are most closely aligned with
Sydney Area Weather Observation Stations . Then you can fine-tune it by taking local measurements and comparing to published observational data. You’ll find that in coastal suburbs the microclimates vary widely, but in Western Sydney it’s pretty uniform, generally with more extremes of hot and cold the further west you go. I’ve worked out that where I live our summer temps and humidity track pretty close to Gosford met station, but in winter temps track Sydney Harbour or about half a degree above. In winter add about one degree for a protected spot, two degrees for an unheated greenhouse, and about 4 degrees for an unheated room in an average Australian home.
Keeping a few seedlings warm in winter
Linear Mode
