I have your H8DGU-LN4F+ with a total of 24 memory slots, now I was planning to fully populate the board with 16 GB Reg. ECC memory and 2 CPU's, which should give me 384 GB (24 x 16GB = 384GB), I see on the mainboard product page that 16GB modules are supported but the maximum memory support is mentioned as 256GB, where are the limitations?
The limitation of 256GB comes from the fact that the AMD Memory controller in the CPU can only support up to 32GB per memory channel, each CPU has 4 memory channels so 4 x 32GB x 2 CPU's = 256GB max.