DX ports are limited to 32 bidirectional channels. This is enough for daisy-chaining 2x DX168 (32 inputs).
In your scenario, you can use DX1 to connect two cascaded DX168, and DX3 to connect the third DX168. DX2 and DX4 on the MixRack are for redundancy only.
I’m more concerned with representing the daisy chained 168s in Director.
As far I can tell I can only access 32 channels in total via director. Or do I just need to patch them anyway, and it’ll sort out when I load the show on actual hardware?