Hi, I always use obj format for models I buy from places like turbosquid and rarely have problems importing with the new 9.0/9.1 obj importer. obj is the best, much better than 3ds or FBX.
But there are some rare cases where an obj would open in Maya, Blender, Photoshop CS but not EI. Usually I resave in Blender or save the model as several parts and it would work. Since Blender is free, maybe you can try that?
- David