Let's first expand the terms inside the parentheses for both (2a-5b)^2 and (6b-3a)^2:

(2a-5b)^2 = (2a-5b)(2a-5b)
= 2a(2a) - 5b(2a) - 5b(2a) + 5b(5b)
= 4a^2 - 10ab - 10ab + 25b^2
= 4a^2 - 20ab + 25b^2

(6b-3a)^2 = (6b-3a)(6b-3a)
= 6b(6b) - 3a(6b) - 3a(6b) + 3a(3a)
= 36b^2 - 18ab - 18ab + 9a^2
= 36b^2 - 36ab + 9a^2

Now, substitute these expanded forms back into the original expression:

9(4a^2 - 20ab + 25b^2) - 64(36b^2 - 36ab + 9a^2)
= 36a^2 - 180ab + 225b^2 - 2304b^2 + 2304ab - 576a^2
= -540ab - 144a^2 - 2079b^2

Therefore, the simplified expression is -540ab - 144a^2 - 2079b^2.