There's plenty of Amaroks already been driven all over Fraser Island.

Lot's of people routinely crossing the Simpson too.

Easiest just to ask an Amarok owner that's already done the trips you're thinking of.

The AusAmarok forum is the place to find the info you're after. AusAmarok - Volkswagen Amarok Forum of Australia & New Zealand

I don't go off road in mine, it's set up for towing my racecar. As a tow vehicle they're great. Concerns about engine capacity only come from people who haven't driven them.