I got new RAM in my hands - 2x4GB Goodram Play 2400 MHz CL15 with slightly lower radiators. It still doesn't fit under my CPU cooler in orientation I have chosen.
Goodram is a Polish brand, which produces well-priced RAM, SSDs, pendrives etc. It's not well known aparat from Poland now, but as I know, they are working on a new brand IRDM, whose products should be available in more countries.
On the photos below you can see where is the problem. Ram fits under the part of radiator, which is marked with blue arrow. What I had to do is to cut the part marked with white arrow.
As I don't have a Dremel I took a hacksaw, a pile and ... someone to help me.
The result is pretty good, I will post a photo next time
The most important is that the computer is working now and I was able to check few things about cable management concept, temperatures and noise. Temperatures are pretty good, but there wasn't any GPU inside the case.
As the motherboard has WiFi and Bluetooth, only two cables (AC for PSU and video output) are required to make it work. BT speaker, WiFi network and remote mouse and keyboard get the job done