Let's first rewrite Quantity A as follows:
Quantity A: \(x^5y^5 = (xy)^5\)
Quantity B: \((xy)^6\)

Given: x < 0 and x > y
Combine to get: y < x < 0

Since x and y are both negative, we can be certain that xy is positive, which means \((xy)^5\) is positive, which means we can safely divide both quantities by \((xy)^5\) to get:
Quantity A: \(\frac{(xy)^5}{(xy)^5} = 1\)
Quantity B: \(\frac{(xy)^6}{(xy)^5} = (xy)^1 = xy\)

At this point, we can see that, if \(x = -0.1\) and \(y = -0.2\), then Quantity A is greater.
Alternatively, if \(x = -1\) and \(y = -2\), then Quantity B is greater.

Answer: D