You should be able to do 6 pin+ 6pin, it's shown in a number of the screenshots, just not listed in the pic of possible combos
one question I have is, what type of screwdriver bit is needed to unscrew the PCIe connectors to change them out, and what types/spacing are installed by default?
I get the feeling I may need to find my precision screwdriver set again, it's around these forums (or my house) somewhere.