Just as tobber said, if you look in the user manual there will be a page that shows you which lanes are shared between which slots

Typically first GPU goes into the highest spot which normally is a x16/x8, then the second card would go into the slot directed by the manual for sli which is usually a x8/x4 or something similar

Then for the sound card you'd want to use a slot the manual says isn't shared with either one of the slots you have a GPU in

Just googling it shows many ppl having had similar issues, most likely from the posts the issue is between the CPU lanes and or the plx chip that handles anything over the lanes that the CPU provides


There's actually a thread about just this in these forums called "In SLI hell - maximus extreme vi" I tried linking it but my phone apparently doesn't feel like it lol


I don't have this exact board and I'm no expert, just info I've seen or learned while researching and looking around