  We examine the dual correspondence between holographic IIB superstring theory
and N=4 super Yang-Mills theory at finite values of the coupling constants. In
particular we analyze a field theory strong-coupling expansion which is the
S-dual of the planar expansion. This expansion arises naturally as the AdS/CFT
dual of the IIB superstring scattering amplitudes given a genus truncation
property due to modular invariance. The space-time structure of the
contributions to the field theory four-point correlation functions obtained
from the IIB scattering elements is investigated in the example of the product
of four conserved stress tensors, and is expressed as an infinite sum of field
theory triangle integrals. The OPE structure of these contributions to the
stress tensor four-point function is analyzed and shown not to give rise to any
poles. Quantization of the string in the background of a five-form field
strength is performed through a covariantized background field approach, and
relations to the N=4 topological string are found.
