Audition, macbook and Scarlett 18i8 2nd gen

I want to use Audition, MacBook Air and Focusrite Scarlett 18i8 2nd gen to record my radio shows and need to record 3-4 channels.

Currently, with Audition, I can only recognize 2 channels. Is there a way to use Audition to record more than 2 channels with this equipment?

Thank you and please advise if you've figured it out or know how.