There is translator out there that may be able to help do this.http://www.okino.com/default.htm
have you tried using STL files instead of JT files.
look at downloading blender and convert your models to OBJ to import into Maya.
We are looking at going to 3Ds studio. So I will be following this thread closely.
We have a program that will export all parts of an assembly to an STL file.