There is no easy way of turning stl's into Iges surfaces. That said there are workarounds:
All of the Delcam software recognise stl as geometry for machining, you just have to set it up properly.
Obviously it's easiest in powermill where stl's are just another piece of geometry to machine.
In FeatureCAM you have to set it up before machining.
I think you should get in touch with your reseller for him to tell you how to do that.
Anyway the easiest way I found to work with 5 Axis Stl's was always PowerMILL - It's a software that cuts through them like butter
Check it out
Adam
Have a great day - Adam
http://www.reliefs3d.com/