If you want to create an aggregate device, you'll be limited to 48Khz sample rate which is what Helix can run on in class compliant mode until we create a mac based audio driver.
USB channels 7-8 are dedicated for reamping, so you can send to those channels from your DAW to re-amp the signal. But yes, it was designed to be the audio interface for that scenario. Check the Global Settings -> Ins and Outs.
BFrenzel's post in Aggregate Device using Helix in OSX was marked as the answer