When a USB is configured with N channels, it is only possible to set each USB jack with 1 to N-1 channels.
So for example :
At 24/48 we have 4 channels for each USB port.
Then It is not possible to route the audio of 2 iPad (USB1, USB2) to a DAW connected to USB3, because only 3 channels can be configured for USB3 output.
Will it be possible sometime ?