HI,
there are a few debian version out there which may nearly work. I am writing this message from an ASUS Tinkerboard running TinkerOS. It is configured minimally. I have also loaded Armbian and Raspbian onto a Raspberry Pi. I am an embedded software engineer. Is the set top box from Pace?
If the processor is ARM, then I can give this a shot for you if you like.
Regards,
Will