I’m using a PSX mat with a PSX to USB adapter. I think that might be causing the problems. Stepmania detects it as 2 separate “Twin USB Joystick” but only the top buttons (start, select, X, O, and up arrow) respond in the input test. I did try adding it to steam and enabling steam controls, but that just adds 2 Xbox controllers to the existing list and stepmania still only sees input from the PSX ones. I did see it in input devices but I’m not experienced enough to know how to muck around with that.

I think my best bet is to get a proper USB mat and hope that just works.