One rig has an open PCIe slot. As for whether you can run more than 9 cards per rig by using additional 1:3 PCIe splitter(s), I honestly don't know because I never tried it. I'll tell you what, if we get to the point in negotiations where you are ready to buy the rigs at an agreed upon price, but you need to know if you can run in excess if 9 cards before you pull the trigger, I'll do a test run for you by switching one of 1:3 splitters over to another rig.