It’s not how the ASIO model works.
If you have 2 of the same audio-interfaces that are able to pair, the ASIO driver of that particular audio interface combines them. That means you can also use that in Cubase.
If you want 2 different devices to work together, you have to use ASIO4ALL.
If both are not a suitable solution for you, you have to buy a new audio interface with enough input and outputs.