Design space exploration can be used to find a power-efficient architectural design for a given application, such as the best suited configuration of a heterogeneous system from soft cores of different types, given area and throughput constraints. We show how to integrate design space exploration into a static scheduling algorithm for a streaming task graph application with parallelizable tasks and solve the resulting combined optimization problem by an integer linear program (ILP). We demonstrate the improvements by our strategy with ARM big and LITTLE soft cores and synthetic task graphs.