I suspect that this question has to be directed to Ableton or Mr.Mac, not to Eventide.
But, have you configured the system as described in the User Manual ? Try connecting the H8000 by itself first of all and confirm that you can get audio in and out of it. Then, be sure that you are creating the Aggregate Device as described in the H8000 User Manual. If possible, try accessing it from another application, like a simple playback or record program.
