Cannot Add Bus at VST Connection (Cubase AI5)

i have 2 units Yamaha n12 mixer, i connect them into one PC to get 24 channels in a row. I use Cubase AI5.
But when i route the Device Ports to the Bus in VST Connection, it’s only allow me to add 16 Mono Bus.
I have tried to record, both of n12 mixers work very good and connected each other. But i need 8 channels more,
Any suggestion how to add more than 16 Mono Bus at VST Connection?

Thanks before,

AI5 was limited to 16 inputs and 16 outputs. Here is a feature comparison chart for the current versions of Cubase that shows the options for Physical Inputs/Outputs

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