The specifications for motherboard model X8DTH-6F indicates support for "seven PCI-E 2.0 x8 slots (all in x16 slots: Slot 1~Slot 7)". Does it have slots that are physically are suitable for x8, but can actually support devices with PCI-E x16 through an extender\adapter?
No, physically they are x16 slots, but the maximum speed supported x8. Thus you can place a x16 card in the slot, but only the x8 speed will be supported.