Pardon my ignorance for omitting, I did that. The Tested Memory List for the board in question list 3 results, one 2400 Samsung and for 2666 one Micron and one Hynix.
The Samsung and the Hynix cost north of 200 EUR and the Mircon around 100 EUR. Naturally i ran for the Mircon, but it's hard to get atm, so I was wondering if it "must be, one of the three"?
Edit: To answer my own question, I've found the answer in the Supermicro X11 E3 Resource
, also thanks for the tip with the manufacturers website and searching in the hardware compat list. Couldn't find one on the Mircon website, but the tip to the Crucial comapt list from the other thread resulted in a newer dimm which is available here.
Sorry for the noise and thanks again.