Found this post whilst looking for a solution.
Sabertooth x58 board
i7 960 3.2ghz
3X4gb Corsair Vengeance
In triple channel it will only find 4gb, when fitting Ram to A1 A2 + B1 finds 8gb. No matter what Ai Tweaker settings, reseating Cpu/Ram most it'll ever post is 8gb. I've tested each...