Sometimes a formula helps. The transmission spectrum T(E) is the integrated transmission coefficients T(E,k) over the 2D Brillouin zone of incident wave vectors k. That is,

[tex]T(E)=\int d\mathbf{k} T(E,\mathbf{k})[/tex]

Of course, in reality the integral is performed as a sum over k-points, that's why you specify the k-point sampling for the transmission spectrum.