Stay away from D-2 steel. It will break your heart and your cutters. For air hardening dies use S-7 steel. For oil hardening use L-6 or O-1 steel; both engrave easily.
Try this site for information on both software and engraving machines. http://www.designscomputed.com/vs3d/index.html They allow you to download the software for free to evaluate it. There is a steep learning curve for mastering 3-D software which is the price you pay for having it in-house.
The cutters needed are micrograin carbide split point v cutters and ball nose cutters.
An alternative to cnc engraving for 3-D is to hand sculpt the design at a 6x1 ratio and use the master to produce a die on a reducing machine such as an Augenstein or Jean Pierre. For 2-D work a pantograph engraver such as the Gorton P1-2 can be used.