I plugged two Intel PRO/1000 PT Quad Port LP Server Adapters on the super riser cards super RSC-R1UU-2E8. But my x8dtu-6F+ only can detect one NIC adapter card. (http://www.supermicro.com/support/resources/Riser/ )
Since the Riser Card does not support Auto Detection so customer has to change the setting manually. For X8DTU-6F+, please go into BIOS setup under Advanced--> PCI-PnP Configuration--> change the Slot J2 PCIe Width x8x8.