If you want to talk to guyZ doing nested pcie switching for TP16 builds this is one of their diagrams:
one super noteworthy thing: you can partition pcie switches into logical switches within the same actual plx chip.
each of these logical switches can have its own x16 link back to the CPU. AND still talk directly between partition 1 and 2 on that plx chip at line rate.
easy way to double your bandwidth and have switch-x32-cpu-x32-switch or just go 3 switches and bypass the cpu entirely.