Also, be advised that infill in S3D is related to and dependent on the location of part on the bed, and not on the shape of the part. Put the part in one location, you get one pattern orientation, on another location, a different pattern orientation. Rotate the part, and all bets are off.
Even if you could output to stl, the analysis would vary wildly, and would not be repeatable.
See my bug report filed today in the troubleshooting and bug report forum for more information. It really is an issue when creating usable parts that are engineered, where you are attempting to leverage the internal structure for some semblance of structure and strength. Having a lot more control over the infill would be a great enhancement for exactly that purpose.