I have tried importing and exporting many 3D files to and from IC. If you are interested in the surfaces, you may need to select 'trimmed surfaces' in IC. After you put the file In the new software you may need to combine the surfaces to recreate your solids. Every system is different.
Also the export type file can select .sat (acis) which is more likely to be a format acceptable to other softwares.
IGES is also a tricky format. It seems to me that you need to know the specific IGES format you are going into. There is online help w/iges translations.
I also like RHINO3D for iges import and export. It has an excellent iges reader. They also have documentation to explain a lot about file translations.
Good Luck
