There is no support for big RAMs (over 16GB/module) on X299 DARK, just like any other X299 chipset based board from any brand due to:
* Consumer CPUs like Core-X series support ONLY unbuffered DIMMs. Currently maximum density of UDIMM DDR4 is 16GByte.
* 32GB, 64GB, 128GB and similar modules are all Registered modules (RDIMM) and have different signaling than UDIMM. System will not post with RDIMM present in the slot.
* Consumer CPUs like Core-X series do not support ECC. ECC require Xeon-W series workstation processor.
* Xeon-W series processor even though electrically and mechanically compatible with X299 boards, will
NOT work in these boards. Unlike previous HEDT platforms (X99, X79, X58) now Intel locked down the use of mismatch segment CPU+PCH.

. Xeon-W require C6xx series chipset board. Mechanically these CPUs are still LGA2066 and can use standard desktop LGA2066-compatible cooler, unlike Socket P platforms.
Hope this helps someone.