Connect multiple USB external soundcards to iPad

Hello,

I am trying to connect 2x USB external soundcards to the USB-C of the iPad. I have a DJing software and I want to connect headphones to one sound card (eg for precueing music) and the speakers to another USB soundcard.

I got a standard USB-C hub and connected the two soundcards there, however iOS will recognize only one at the time.

How can I get the two output simultaneously?

Thanks for providing more information.