What's the max number of audios you've been able to play from an SD card, either directly on the Teensy or on the Audio Shield?

I ask because I saw this Wav Trigger from Robertsonics. They say it "supports playing and mixing 14 tracks with an average speed microSD card". Those tracks are stereo. Now, that seems amazing, but kind of impossible to me. Even more, they have a Tsunami board that they say can play 18 stereo tracks at the same time. I really wonder how they do it. I read the schematics and neither of those boards has any external ram where they could store the files. It really baffles me.

Does anyone have an idea of how those polyphonic capabilities could be approached with Teensy boards and shields?
Thank you all very much for your time . I hope you have a nice day.

They say it has a minimum 8 ms delay that can be up to 12 ms. Maybe it has a bigger buffer, so they can read longer chunks from the SDcard and do it faster? Even then, I'm not sure how that could get you 14-18 stereo tracks at the same time.