  Recently, it has been proposed that the S-matrix elements on the world volume
of an abelian D$_3$-brane are consistent with the Ward identity associated with
the S-duality. In this paper we extend this study to the case of multiple
D$_3$-branes. We speculate that the S-matrix elements are consistent with the
S-dual Ward identity irrespective of the ordering of the external states.
Imposing this symmetry on the particular case of the S-matrix element of one
Kalb-Ramond, one transverse scalar and two nonabelian gauge bosons, we will
find the linear S-duality transformation of the commutator of two nonabelian
gauge field strengths. Using this transformation and the standard S-duality
transformations of the supergravity fields, all other nonabelian S-matrix
elements of one closed and three open string states can be found by the
S-duality proposal. We will show that the predicted S-matrix elements are
reproduced exactly by explicit calculations.
