I have a DQ77KB motherboard running ESXi 5.5, and I had problems initially installing ESXi (5.1 it was at the time) and trying to pass through the onboard USB ports. Seemed like whichever port I tried to pass through, all of them would end up being unavailable for the keyboard and mouse. I ended up getting a separate USB 3 add-in card and passing that through to the VMs, and I left the onboard ports alone. One thing that may have something to do with it is the Intel-AMT stuff may be interfering as it also needs to monitor the on board USB ports in order to simulate keyboard presses and mouse movements when someone signs into the machine remotely. I never did this because I needed the AMT support as the computer is in a remote location, but if it's in a local location you might try disabling all the AMT stuff in the bios.