Could you clarify your question?
-Do you mean that you want to export from XSI? If so, ask the question in the XSI forum.
-Do you want to export into dotXSI format? If so, you can export with this format if you have Softimage version 3.9.1 and above.
All I can say is that all available export formats can be found in Tools > Export > Object. Also, there are some utilities to export to Lightwave and maybe some other packages at Ed Harriss's website (www.EdHarriss.com)
Hope this helps
Bernard Lebel