[en] By generalizing recently introduced quantities (referred to as 'thermal transmissivities'), the usual duality results concerning the pure Z(N) spin systems (including the standard Ising and Potts models) are recovered as well as generalized gauge systems (plaquettes or more complex simplex) in d- dimensional hypercubic lattices. The essential relationship between duality and simple series-parallel transformation becomes evident. The simplicity of the equations enables conjectures on the approximate critical frontier of the diluted version of the above systems, including some particular asymptotic behaviours which are believed to be exact. As an illustration the d = 2 diluted Z(4) spin system is discussed in some detail: for those regions where exact results are available the agreement is satisfactory. (Author)