Your local DNSP (Energex) mandates that you can only have 5kW of inverters per phase. I’m assuming you have been quoted Enphase S270 270W micro inverters. That means a maximum of 18 micro inverters are allowed on a single phase (18 x 270 = 4,860W).
But there is still a way to get up to 6.6kW of panels on your roof and not break any rules.
And that is to use panels that are up to 133% bigger than the 270W micro inverters. i.e you can use panels up to 359W.
For example if you used 18 x 330W panels you would have 5.94kW of panels.
You can do this because of the ‘oversizing rule’ as described here.
Other FAQs that may help: