GarageBand - How Do I Playback Multiple Tracks via USB?

I have successfully connected my Soundcraft Performer 2 digital audio console's 32 channel USB I/O card to my MB Pro and recorded 21 instrument and vocal tracks for a live band that I mixed recently. However, when I try to play the tracks back into my console from Garageband, I am only getting 2 channels that sound like a stereo mix of the recording. I want to send all the tracks to the console so that I can use them for a virtual soundcheck, but I can't figure out how to do it, so I'm looking for some help. All I have found so far is information on how to locate the WAV files for my individual tracks so that I can import them into another app like Reaper and use it for multitrack playback, but I'd rather not do that if there is a way to get Garageband to playback more than 2 channels via USB.

FWIW I'm running Mojave because I like iTunes :) and I'm a Garageband newbie.