How can I configure generic SNES-style USB controllers for Steam Link?

[Rivalsonsaway]

After reviewing several posts, I see that there's a list of officially supported controllers for Steam Link. I'm hoping for your help configuring unsupported controllers, if there's a way to do it. The trick is that, whatever I set up, I'd like the configuration to be saved and to work the next time I connect through Steam Link (so I don't have to do it each time I play).

I have a Retropie with four generic SNES-style USB controllers attached. I have Steam Link installed on the Retropie. I'm able to connect the pi to Steam on my computer. However, Steam doesn't recognize the controllers.

I have an extra PS4 controller that works okay with this setup, but I'd really like to use the generic SNES controllers if it's possible.