Kaby Lake desktop have upped the number of PCIe lanes by 20% if the Xeons do the same then you just about have enough -- your list above is 112 lanes, 48*1.2=57

Kaby Lake desktop have upped the number of PCIe lanes by 20% if the Xeons do the same then you just about have enough -- your list above is 112 lanes, 48*1.2=57.6 and so 56 is not unreasonable.