Best guess? Whichever account gave account 6 permission to play their game.
Either account 1, 2, 3, 4 or 5 will be the user that gives 6 the permission to play their game, so it follows they're the one that (I'm assuming) will get banned also. It's a good question you raise and I'd be interested to know for sure myself.
Damn, looks like I'm a little late to the party. I'm kinda glad I missed the sale actually because it's really not something I could justify buying right now.
I hope everyone that has bought one enjoys their Deck ๐