In Cain’s plan, 999 is a temporary bridge to the Fair Tax. Eventually the 9% income tax and 9% corporate tax are eliminated. In the meanwhile, it takes 2/3 majority to change the rates.
Because the corporate rates are going from 35% down to 9%, the actual cost of the item comes down so it all balances out. This section of the plan is well studied and is presented in fairtax.org
The 999 is middle ground to bring the flat tax and fair tax proponents together.
His 9-9-9 plan would be dead-dead-dead in Congress. It’s a campaign gimmick. That’s all it is.