As far as i know, Softimage and Max are the only ones that have the necessary tools to create a valid .XSI file for the compiler.
The XSI mod tools should be free, they only ask a few questions for registration.
As stated on their website:
"Scene files can be saved to a special .exp file format so they can be loaded into the SOFTIMAGE| XSI Mod Tool. XSI Mod Tool (.exp) files will not load in the commercial version of SOFTIMAGE|XSI."