My DD has this.

You'll need to see an audiologist first. You can self refer. Do you have a hearing centre around you? They'd be the best bet.
We did sound integration therapy and Extra Lesson with a private psychologist. There are only two pyschs that I know of who do this, one in Sydney and the other in Canberra. There could also be one in Melbourne, but I would have to ask around. You can buy the at home system from "integrated sound systems" but it's quite expensive, but my DD did improve with it significantly. A white noise generator is good for times when they need to concentrate hard on something. And sometimes visual to do lists save a LOT of frustration as you can give more than one or two instructions at a time.