there's rly no motherboard that can handle 3 x16 PCI-E 3.0, the most is 2 x16 PCI-E 3.0 w/ 1 x8.
AMD's best is the ASUS 990FX Sabertooth Gen3 R2.0 which has 2 x16 PCI-E 3.0. This is a limited production mobo which only work in PCI-E 3.0 and only the Vishera/Piledriver CPU will support it.