I have no idea whether this has been brought up in the past, but apparently STK doesn't recognize input devices when passed through a steam link to the system.
While it works flawlessly on countless other games, STK only recognizes gamepads when plugged in locally at the pc, then it works like a charm. As soon as the gamepad is plugged into the steam link, STK doesn't recognize a gamepad being used and the pad can't be used ingame.
Using the Steam Controller it's possible to use mouse+keyboard layout to get some controls to the game, but the sensitivity is horrid as always when using keyboard controls in a racing game, and my kids would like to use the xbox controllers, but so far all attempts to make this thing work have been foiled.
Maybe someone brighter than me can figure out a solution, as it's at least somewhat likely for the popularity of the steam link hardware to increase some more in future (Gaming on a 65" HDR TV is really kickass).
Have a great and happy xmas, everyone!