Logic Pro X: Logic only sees one USB audio interface device
If you install multiple USB audio interfaces of the same model, Logic only offers one of them in the Audio > Devices panel of the preferences. This occurs even if the device driver supports multiple instances of the device.
If you want to use multiple instances of a USB audio device in Logic, you must create an Aggregate Device comprising each instance of the audio hardware in Audio MIDI Setup. For information on how to create and configure an aggregate device, see this article.
Once you created the Aggregate Device, select it as the input and output device Audio > Devices in Logic's preference panel.