I am thinking of getting Crucial 32GB Kit (2x16GB) DDR3-1866 RDIMM 1.5V Memory For Mac Pro Systems (Late 2013) CT2K16G3R186DM at Amazon for $400 instead of Apple's RAM because I can later add 2 more sticks if I need/want 64GB RAM. At the 64GB RAM level, Apple says the RAM must be registered, because the memory controller can't handle a large amount of RAM? If I mix different brands of registered RAM, could there be issues? For my current 2009 Mac Pro I bought RAM in sticks of 3, because the 4,1 Mac Pro is triple channel. Is the nMP dual channel?