+1 to this. OP is using the wrong flavor of compression for the task at hand. OP, look up sparse bitmaps.

Are these really sparse? He is working with Go boards. Go games are usually hundreds of moves and by the end of the game, most of the board will be populated with stones, so on average somewhere under half of all recorded intersections will have stones (the crowded late game positions balance the empty early game positions). Sparse matrix representations usually require a lot of sparsity to shine, I was under the impression.