Thanks for the reply. I was looking into the Pi as well, and think you're right in saying that is the way to go.
I didn't install any software for the Helix to work with the iOS (ie: Apple) device, but I'm sure that's because it is a USB class compliant device, which supports 8x8 audio and MIDI.
My desired signal flow is 1/8" stereo analog audio in from an external source (sound board, MP3 player, stage monitoring signal, etc ...), and two channels of USB audio out (into the Helix). There's a particular way the Helix handles USB audio in on channels 1 and 2 which I want to feed an analog signal directly into.
When the Helix is connected, it essentially becomes the sound card for the connected device. I believe the Pi can do this, since I'm dealing with a class compliant device, but I'm not sure how Linux handles it. When connected, there would be 2 sound cards. The integrated one in the Pi, for the incoming analog audio, and then the Helix as the second sound card (connected VIA USB) for the outgoing digital audio.
Thanks for the info, I'll go do some research on the Pi and see what I can come up with.