Probably the best thing to do is run a measurement curve and determine what transfer function you want them to use. You don't need a stepped baffle if you have a crossover that can vary the delay on the tweeter section.I'll note that I usually suggest the DSP crossovers because they give you more flexibility. With the Marchand and others that only offer symmetrical slopes (excluding the baffle step feature)a parametric EQ will help quite a bit.