I tried using a raspberry pi 3B and the same thing.
The aplay -l command did not return the card1 info.
This is beginning to look like a case of I can't get there from here. Maybe someone else will chime in and say they did it or it didn't work for them.
I guess a couple of things to try.
1. Make an image of your SD card and upload it.
2. Did you do exactly what you listed including downloading the "latest" Buster and making a fresh SD card and downloading n7nix from the GitHub repository? Maybe try it on a Pi4 although I have tried it on both. It only takes about an hour depending on your internet speed and I have done it about 10 times.
Frank - K0FEI