I’ve run out of PCIe slots on my 2007 MacPro 2x2.66 and I’ve found this,
External PCIe Expansion KIT - do you reckon it would work?
I’ve emailed them and it’s only $200 USD which is a tenth of the price of a Magma case
External PCIe Expansion
PCIe x4 to four PCIe x1 Expansion Backplane Kit