Hi RemHep, I am sorry you for this trouble.
Based on the information you provided I believe that the cause of the issue itself lies on this digital-to-analog conversion you are using. You probably have more chances of getting it working with a DP to HDMI cable.
It is also a good practice to take note of the original BIOS version before updating because sometimes it is necessary to follow specific update instructions in the BIOS release notes before you can get to the latest version. I usually recommend incremental updates.
The main difference between the kit and the board is that the kit comes with the chassis (and other internal components) while the board does not.