I have a Presonus AudioBox USB device, connected to a USB 3 port, that supports both MIDI and Audio input. When I launch JACK and open the connection list from QJackCtl, I can see that the AudioBox device itself is detected, because I can see the MIDI input. However the audio line-in input is not detected. If I open Audacity without JACK running, the audio input is available in the input device list. I've verified that I can record signal from my guitar through the AudioBox's line-in in Audacity.
What this tells me is that the device is working correctly, and seems to be detected by ALSA, but for some reason it is not being detected by JACK?
Does anyone have any idea what possible causes of this might be?