hey i have the same problem i filled all slot with ram and CPUZ says i have 18gb ram where windows says i only have 6. i have the Rampage Gene 2. if you get an answer please let me know as well. i am gonna try to get some help from the asus and see if i get somewhere i will keep you posted.
did you get any answer yet ?;
With my problem, i ultimately figger out that one of my RAM sticks was not functioning., and that was all the reason for the faulty diagnostic program of windows and CPU-Z;
So , may be you should check the RAM sticks, one for one , in order to find out which one does not function well;
Hope this will help you;