12 month multiple entry max stay 180 days

I am here on a 6mth 2 entry with max stay 90 days, I will return to Australia to renew it in July I was thinking about a 6 or 12 month multiple entry max stay 180 days , but from what I have read the max stay under it is 2 months, is this the case?/ what is the best way to have extended time here, I live defacto with my Chinese wife. the cost of returning for renewals is ridiculous. any help please