What are you using to create .dxf's for SheetCAM? You could draw lines for each pass, with each pass on a different layer, and set different depths for each layer (pass) in SheetCAM. As for the math for the angle, just draw it in your CAD program, and figure out the stedown based on the stepover your using.
The above is assuming you have a CAD program. IF not, try this free one. http://www.a9tech.com/products/a9cad/