Hi Mr.Schorsch,
I have to deal with CAD-data a lot everyday, in Max the body objects can get quite buggy though.
Then truth is (as far as I know) the Body Objects plugin implemented in Max is a cut-down version of the PowerNurbs package.
After having bought the full one i didn't have any issues in Max while importing STEP or IGES Data (although depending on your package you might need to buy a special version of PowerNurbs, e.g Jupitor Translator [JT]is not included in the PowerTranslators Pro).
There are 30-days trial versions on their page, if you find time check it out! Up till now this was the most ideal way to handle CAD data in Max, without going through the pain of data conversion.
As far it goes for Corona, it works perfectly with PowerTranslators Pro, i have done a lot of tests. All but one produced nice clean renderings with no normal problems. The one time where it went wrong, it was obviously due to bad Siemens NX > STEP conversion. Nevertheless this case is very interesting, because the same geometry rendered clean in Alpha 0.6, in 1.0 it came out broken. I will dig up some screenshots on monday and post them here for comparison, perhaps you guys know the cause.
CheerZ,
G.S.