Most of us who mill PCBs on a regular basis use http://flatcam.org/ as it works extremely well, it updated often with new features and best of all, is FREE. It reads both GERBER and EAGLE files so it pretty much works with everything. 2 sided milling is also easy. Might one to give it a look. A walk through for it can be found here: How to mill a through hole PCB | Inventables