motherboard with 8 pcie slots: PCI Express - Wikipedia. Memory Slots - 8｜Motherboards｜ASUS Singapore. DIMM - Wikipedia.
Asus announces B250 Mining Expert motherboard with 19 PCIe
slots and triple 24-pin power connectors.
>Finding Motherboard with 8 Mem Slots for AMD Ryze.
The MSI X79A-GD65 (8D) is a high-end X79 motherboard featuring eight DDR3
DIMM slots and claims to be the first motherboard with support for PCIe 3.0.