Mojo,
to circle the problem it would be good, to try if the Pcie port´s are working.
Sure you are for some days now trying everything to start this......(sh........ ).
I don´t know if you have the po(i)ssibility to lend a pci-e card from a friend or so,
or you can try other things to male sure that the mb is not defect.
Sorry for asking so much questions but (and this again)
have you tried to expand-disable all network- ,lan and usb devices and fw card at one point and
starting your system without all that and then
implemented the fw card and started the system?
I guess yes!
Pragi