In my experience many PCIe extenders—even those extending x1 to x16 with a separate power plug—do not short the presence detect pins. Also, I don't think the f

In my experience many PCIe extenders—even those extending x1 to x16 with a separate power plug—do not short the presence detect pins. Also, I don't think the fact AMD cards work does not mean shorting won't be required for other cards. The PCIe initialization process is complex enough that there could be a variety of reasons why AMD cards can be down-plugged but not your Titan X. In short (pun intended) I would highly recommend you to try shorting if you feel confident in doing it.