Idk, I found a few sites that keep saying two PCI-Express 8x slots. Where are you seeing the x16?
Expansion slots 6 available (1x PCI-X 133 MHz Active PCI-X, 2x PCI-X 100
MHz, 2x PCI-Express, 1x 32-bit/33 MHz)
As that is an old pdf I'm assuming they mean two x16 slots as there were a few other manufactures describing dual x16 slot boards that way at the time, I bought a couple!