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OT: Can a USB audio interface feed another USB audio interface?
I am not sure if what I am trying to do is possible. I am using a Line6 Amplifi as (i) a modeling amp (2) speaker (3) USB interface which attached via a powered hub to my iPad. Unfortunately, the Amplifi doesn't have a microphone input. What I tried to do is use a Presonus USB interface to take in the microphone signal and output to the USB hub and then into the Amplifi. Unfortunately, it seems to want to "take over" the connection and route the audio to its outputs, rather than allow the Line6 to drive its speakers. Do you know if the Presonus or others can be simplified so they only digitize and send along the audio input, rather than trying to manage the session? (I just realized the Presonus is USB powered, which might make this harder. Perhaps a plug-powered interface could operate to digitize the audio without controlling the session).
I could accomplish something similar with a mixer and route the output to an aux-in on the Line6, but that seems less elegant.
Thanks in advance.

Comments
You can plug only two different audio interfaces if one has only inputs and the other only has outputs. If one of them has both usually takes the control over full core audio driver itself. Also if you want to use surface controller with integrated audio interface, first plug first served and viceversa let you use the midi part but avoidding the audio side... so take it in mind when you make your test.
@Dubbylabby Thank you. I decided to just use the output from from my vocal / guitar pedal into the aux in on the Amplifi. This still shows up as in input on the iPad which is what I wanted.