I'm from Sydney Australia and this is my first post

I recently had my two 60yr old Iron Bark Eucalyptus trees cut down because they were both infected with Bracket Fungus. I was told by a tree lopper that the fungus will still be in the ground even after the trees have gone and that the ground will have to be treated with a fungicide before I plant anything in that spot.
The problem I have is the original owners of this home built the ground level up around the base of these trees by about 600mm which means to get the the root system I would have to dig down more than a meter, to be able to apply the fungicide.

If anyone knows anything about bracket fungus and how to treat it, I would really appreciate any suggestions on how to tackle this problem.
The tree that I want to plant in place of the Eucalpyptus trees is a "Forest Pansy". It's a beautiful tree that I've only recently discovered and believe its native to America. I've read conflicting information about the climate zone this tree will do well in and was wondering if anyone can shed some light on this for me.
Western Sydney has a fairly temperate sub tropical climate. We can get light frosts in winter and very hot and humid summers. Will this tree do well in this type of climate? I've read that they can be found in Florida so I figured it would do okay here, but I've also read that they are more suited to a colder climates, so I'm not sure if I should give it a go or not.
I would appreciate any advise you may have and thank you for reading my post

All the best
Joanne