I have looked through every article i can find on the Rebels sale. Your point that the the Rebels get $6million and the other franchises get significantly more does not line up. The only thing i could find is that each club receives $6million up from $4.5 million when the broad cast agreement was boosted.
While the Rebels might receive an additional $900,000 from the ARU in the initial year of the arrangement, the deal peters out so dramatically that in year five, the Melbourne club will receive only .
This is a snippet from a paywalled article from the Australian dated April 1 2016 titled ARU funds new Rebels owner to stay afloat.
Then theres this article confirming the Rebels will receive an additional $6 million over the 1st 5 years of the private ownership deal.
http://www.sportsbusinessdaily.com/Global/Issues/2016/04/01/Franchises/Melbourne-Rebels.aspx
So the real figure is the Rebels will receive $12 million in support while the other franchises receive $6 million from the broadcast deal.