User cannot replace the riser card, RSC-R2UU-2E4R with RSC-R2UU-2E8. The PCI slot, SXB2 where the riser card install is PCI-E x8 slot. Riser card, RSC-R2UU-2E8, did not contain a chip which has PCI bridge to allow 2 PCI-E x8 slot sharing one PCI-E x8 slot.