Question about connecting an external source while also using the system sound (Mac)

Hi!

I am using the latest version of Audition and I am trying to have it record (and playback) sound from my system and a Rockville RockMix 6FX mixer. I have downloaded Blackhole and can hear and record the audio from both, but there is a massive echo. From what I have read I am recording both the sound going out and the sound coming in.

I'm hopeful that there is a way to resolve this, as I need to hear all the elements (it's for a podcast and the guest will be connected via the Mac running audition, I need the mixer for multiple elements (microphone, another computer for sound, etc.) and need to be able to hear playback of the recording through the computer so I can hear the person speaking over my computer.

The reason I can't run everything from the Mac is that I am also using video and need to capture the screen to get the video of the guests.

Any help would be much appreciated! Thanks.