Just going to add a few things
100%
-Since it has FCC approval there should be a record that might give a clue when this thing was planned.
-I think its safe to assume these are the controllers that came with this system. which doesn't make sense.....but does it if its a prototype?
-I wonder if it plays turbografx or pc engine games...or both
-Did anyone contact the seller asking him to contact the buyer to try and get some more information?
And some ideas ranging in possibility
-It could be a prototype to save costs. I know Turbo Duo sales were on life support, but sometimes different teams are working on different products. It's possible when the Duo R was being designed early plans for US implementation was green lit resulting in this unit, and possibly more that were scrapped.
-Maybe it was a unit being planned by possible partnership with another company like Majesco did with Sega products.
-There has been multiple "lost" or unknown consoles and prototypes discovered with the SNES CD last year so although i'm surprised, im not shocked.
-As far as it being a unit to work in conjunction with a computer, I would put that at unlikely. Although at least this was the time to do it.
Examples
3DO Blaster (Add on for the computer to play 3do games)
Diamond Edge 3d (Card that allowed PC play of saturn ports also used regular saturn controllers)
And finally the most likely reason
