I recommend using PFPX http://www.flightsimsoft.com/pfpx/ to plan your routes, it’ll produce a file that FSX’s flight planner understands, and the NGX. However, FSX’s ATC doesn’t understand SIDs and STARs and will always vector you in. I have Radar Contact, but I wish I’d bought PRO-ATC/X instead http://www.pointsoftware.de/proatcx_e/index.html as it can handle a change of runway better, similar to how it would happen in the real world. But both Radar Contact or PRO-ATC/X will understand your plan better than FSX.