Every island will need to be detached.
Here's a tip to speed up the process. At least in Max anyway, not sure if it also works in GMax. Switch the mesh to an Editable Poly, then add an Unwrap UVW modifier on top. Click the button to open the UV editor, switch to the Face Sub-Object mode and tick the Select Element button. That will allow you to easily select all of an island at once, including overlaps. Now in the hierarchy stack, unfold the Editable Poly. With an island selected in the UV editor, click on Element under the Editable Poly. You should switch to the Editable Poly with the island polys still actively selected. You can't do this with an Editable Mesh.
Not in GMax format obviously. But you can use an OBJ export script to get them into a format Blender can import.