FBX Instance problem

i use 3DSMAX and create two cube by instance,
i give them the different materials

and export them to fbx with Preserve Instance

in fbxfile they use same geometry and different materials

but after i import this fbx to unity, the two cube just use the same material

anyone help me?

[72655-2cubes-2color-ascii-2name.zip|72655]

this is the cube