We Recommend usng this guide on a fresh install of Raspbian Desktop, once your desktop is up and running and connected to the internet you will want to install the Steamlink Client
You can do that using the following commands on a terminal
curl -#Of http://media.steampowered.com/steamlink/rpi/steamlink_1.0.7_armhf.deb sudo dpkg -i steamlink_1.0.7_armhf.deb
Then you will want to follow the guide at https://github.com/petrockblog/SNESDev-RPi to install download and install the SNESDev drivers. You'll want to make sure you install SNESDev as a service, and update the following items in the /etc/snesdev.cfg" file.
We now recommend rebooting your Raspberry Pi, you can now start the Steamlink Client under 'Games' in the main menu. You should now see the "SNES-to-Gamepad Device" as a usable input within the program, you can now configure the UI and button layout to your liking and connect to your Steam streaming computer.