I think you'll might be missing a trick here..  Should be able to load the whole thing with Nvidia's, plus some!  You just have to do it in the right order. load in numbers that wont trip the switch from x2, x4, x8, x16...    This means you should load just x1 card per section, then x3 card, x7 cards.. So you don't swicth it's limits (if this section has x4 then that section limits to x8,x4,x2 or x1)  once completed x3 cards in each section, the empty slots can be filled without limiting the others, because it can't limit to x2 with x3 in use) Something like that anyway   Think CPU lanes too