It has only 1 cable with 2 branches.
My initial idea was to use the 8 pin CPU connector with an extension, where I cut the cables at one end and just plug them in the board connector, but something went really bad there.
Now I have connected both branches of the same PCI-E cable and all seems to be working just fine - I was measuring temps with an IR thermometer for like 20 minutes.
Obviously I would prefer to use the CPU cable, but I would not risk it with these cheap quality extension cables.

Now I have to find a way to use it.