got some news. I don’t think, that it might change something, but who knows.
I added in grub the option “insmod progress” (which I found by googling somewhere). It should show, if kernel and initrd do load or not and now I can see, that the vmlinuz and initrd are loading to 100% and after that it hangs. So it looks like the kernel loads but then stucks.
As said before, I don’t think that this might change something in regards to further tests with my actual mobo, but I didn’t want to left that out …