Use all the digits 1 to 9 create three 3-digit numbers, which, when multiplied together creates the highest value possible.

(In reply to

re(3): How to do! by David Shin)

I think I know what you might have meant. Since the hundreds digits are {7,8,9}, the tens digits are {4,5,6}, and the ones digits are {1,2,3}, the sum IS fixed at 2556. Then your approach is certainly a valid verification.