I think you can use the download version unsubbed in system tournaments. When i was watching a while back someone was using the download version unsubbed, i dont play in them so i cant be too sure if you still can though.

Could be that it was a subscriber only tournament, and if you're not a subscriber you can't participate. 

Or

If it was a tournament where everyone could participate, you could have been on the pc game without paying for subscription meaning again you can't play games. 

Hope that helps :)