The capitalist in your Box analogy is introduced as 'a millionaire,' an owner of pre-existing capitalist.
As you no doubt have determined by exposure to the votaries of capitalism on this debate board, many people focus instead on the 'self-made man' so conspicuous in capitalist media. Bill Gates, as a representative of capital, has replaced the Rockerfeller Empire in most people's minds.
Your analogy must anticipate that.
Marx's theory of value, I think, is still the perfect description of the problem. Because Gates, after all, is as much a thief as Rockerfeller's heirs ever were.