Hi Bogdan,
I am running my KGPE-D16 with 2x6276 and 16 of these 8GB Samsung RDIMMs:
M393B1K70DH0-YK0
They work fine in coreboot. If you want to run them at 1600MHz, you need to raise the voltage to 1.5V even if the vendor bios clocks them at 1600MHz with 1.35V. They work fine in this setting as well, although this is out-of-spec according to Timothy Pearson. I have no idea how to check if they run in quadchannel but appreciate any hints. You can find more info on this thread:
https://mail.coreboot.org/pipermail/coreboot/2017-February/083151.html
Please be aware that power consumption in idle on the KGPE-D16 is still a major issue with coreboot (~150W with coreboot while ~80W with vendor bios in dual-cpu config):
https://mail.coreboot.org/pipermail/coreboot/2017-February/083195.html
Also, if running the board populated with DIMMs in all slots the best bootup time for coreboot I could get was around 30s:
https://mail.coreboot.org/pipermail/coreboot/2017-March/083595.html
On the contrary, with just 2 UDIMMs, it booted up almost instantly. Please consider this as well when making the decision.
Yet, I am happy to welcome more KGPE-D16 users and share experience.
Cheers, Daniel