Can you point to a specific motherboard? 16 separate PCIe links of any width sounds rather high for a consumer platform.
C9X299-RPGF
https://www.supermicro.com/en/products/motherboard/C9X299-RP...
C9X299-RPGF
https://www.supermicro.com/en/products/motherboard/C9X299-RP...