Apex multilevel destruction question

I’m trying to build a crate that when damaged breaks so that the sides fall off first, and then the sides break into individual planks.

-Ignore the bouncing

Here’s my Unity demo of the crate

The built in fracture tools can only work with the first destruction level, so I have to use the Apex tools. If I create the model in Maya LT so the the sides are a child of the crate, the sides will break off of the crate but the crate (destruction level 0) will still be in the scene. If I separate the crate, sides, and planks into 3 separate meshes and import them Apex will only apply them to destruction depth 0 and 1. Has anyone had any success with multilevel fbx imports into Apex?