You're very welcome, Eugen.
Unfortunately, I am not an expert on the Workstations, like I am with the general business desktops such as the dc7xxx, and 8xxx Elites.
I think your model has different BIOS settings such as RAID + AHCI, then what I am familiar with.
If you look inside those file folders I attached yesterday, you will see that one of them contains multiple driver setup information files to choose from.
What you could try is to install W10, and even if it doesn't activate (it probably won't if you didn't take the free upgrade to W10), at least you will be able to go into the device manager and get the hardware ID's for the AHCI or RAID controllers, and then I can try and figure out exactly what storage controller driver you need.
You can make a W10 USB installer from the link below using the media creation tool on another Windows PC.
You will need an 8 GB flash drive for that.
https://www.microsoft.com/en-us/software-download/windows10
if you are asked to enter a product key, check the 'skip' box, and W10 should install.