So......
The audio probe helped a lot. Found that audio wasn't even getting to the first resistor in the circuit. So here I found stupid issue one: the diagram on the website has the tip and ring backwards, at least for me. I don't have a TRS cable, so that probably changes the wiring for me. I think.
I followed the audio probe to the very end of the circuit but still wasn't getting any sound out. So here's stupid issue two: I didn't add enough solder on the output wire. Despite it looking ok, it still wasn't a good enough connection.
Thanks all for putting up with my stupidity.... Guess it takes failure and stupid issues to learn more.