Hi Brettski,
Firstly please ensure that you are using the genuine apple camera connection kit to link the two devices. You will then need to select the
18i8 as the audio input device in Garage Band and then create 4 mono audio tracks monitoring inputs 1-4 of the
18i8. You then need to record arm every track (I would check the signal is getting through first) and hit record. This will then record all 4 of the 18i8s combi inputs (on the front of the device).
If you are still having a problem doing this I would recommend getting in touch with us directly and opening a support ticket by navigating to
https://support.focusrite.com/hc/en-gb/requests/new
Please include any screenshots etc that will help us to see where you are getting stuck.
Best regards,
Alex Bull // Focusrite Tech Support