Ok so I spoke to Gigabyte about whether BIOS updates to the PH67-DS3-B3 would enable VT-d and they say - 'Award bios does not support VT-D unfortunately. Only UEFI bios which is installed on new MB's support it.'
This means I must buy a new board to complete my task. I also believe that if I upgrade my motherboard to a board that has UEFI, I will encounter problems booting my current ESXi system even if the board is fairly similar. This leaves me with no choice now but to build a 2nd system. Wish I had bought the correct board in the 1st place now. Doh.