According to the meaning of the question, "Xiong" = 1, "Da" × "Er" < 10, then "Da+Er" <10; "big" × "two" > 9, then "big"+"two" < 9;

Enumeration: "Xiong Er" = 10, brother is 0, "Xiong Da" has no value, because different Chinese characters represent different numbers;

"Xiong Er" = 12, "Xiong Da" can be 13, 14, 15, 16.

"Xiong Er" = 13, "Xiong Da" can be 14, 15 (omitted, numbers are repeated);

Xiong Er = 14, Xiong Da is worthless.

So the sum of the three digits represented by Brother Xiong is:12× (13+14+15)+13×14 = 686.

So the answer is: 686.