Looks like there are 6 PCIE slots, + 1 PCI. But a little digging:
The manual for the vanilla D3H states that if the 4x slot is in use the 1x are slots are unusable.
1x PCI Express x16 slot, running at x4
(PCIEX4)
*
The PCIEX4 slot shares bandwidth with
all PCI Express x1 slots.
All PCI Express x1 slots will become unavailable when a PCIe x4 expansion card is installed.
*
When installing a x8 or above card in the PCIEX4
slot, make sure to set PCIE Slot Configuration in BIOS Setup to x4.
3 x PCI Express x1 slots (The PCIEX4 and PCI Express x1
slots conform to PCI Express 2.0 standard.)
Not sure if BIOS updates will fix this