From my reading on this it seems that early 16GB DIMMS were quad rank and seemed to be the general explanation, the guess was that dual rank DIMMS would likely work. I have no opinion on the matter because I just don't know. I have a dual rank 16GB DIMM in mine now over the next month or so I'll add 2 more. When that's done, I'll ask my local guy if he'll take the 4th one back. I don't need 64GB of RAM and the DIMMS cost 105 euro a pop, I can't/don't want to eat that 4th stick even if it does work.
These are what I'm putting in:
16384MB Samsung M393B2G70BH0-CK0
http://www.arlt.com/Hardware/PC-Kom...er/DDR3/16384MB-Samsung-M393B2G70BH0-CK0.html