I don't see a reason why any of your requirements wouldn't pass.
File formats in Rhino. I do STL's sometimes. There are a lot of post processors already and they are easy to edit. A Trunnion table is just another simultaneous 4th axis setup. As long as Mach 3 can manage that it will work fine.
Why don't you download a Rhino Demo and MadCAM Evaluation and try it out?