In this paper we present a method for extending the interval-based mixed integer nonlinear programming Superstructure (IBMS) model of Isafiade and Fraser [Chem. Eng. Res. Des. 2008, 86, 245-257; 909-924] for heat and mass exchanger networks synthesis to handle split streams going through two or more exchangers in series. A major shortcoming of the IBMS generation approach is that only parallel heat/mass exchange call take place for split streams. Individual split stream branches cannot exchange heat/mass in more than one exchanger since split streams must be mixed immediately after exchanging heat/mass in order to define the next interval boundary temperature/composition. A major deficiency of this is the tendency for the search space to be reduced thereby limiting the number of possible network configurations which call be generated. A method for overcoming this shortcoming is presented in this paper. The approach involves splitting every Stream into subsuperstructures just before it enters into the parent Superstructure and Subsequently mixing the split streams while exiting the subsuperstructures. The new method has been applied to literature example problems to demonstrate its benefits.