According to the manual, it like 6 slots, but I could be wrong.

Slots
  2x PCIe 3.0 x16 slots
  1x PCIe 2.0 x16 slot
  - PCI_E7 supports up to PCIe x4 speed
  4x PCIe 2.0 x1 slots
  - When PCI_E4 is installed, PCI_E3 will be no function.

PCI_E1  x1
PCI_E2  3.0x16
PCI_E3/PCI_E4  x1 (shared)
PCI_E5  3.0x16
PCI_E6  x1
PCI_E7  2.0x16