I have tried Xfire in that combination mate.
Its not something that a new board will help you with, you will have the same problems in that configuration I suspect. I have two boards here and neither work well in that configuration as is you have to play with the PCI offsets and CPU offsets. I suspect also as your graphics card is new the PCI 3.0 codes for that hardware will be in very early revision. I found with 7970 Trifire it got better with Bios revisions and easier to tune. I dont have 3 680 here to test only one sadly but the way your trying to set em up is a rocky road that takes time to get it correct.
Make sure you have the PCI EX EZ plug, pluged firmly in.
Now here is what you can try initially. Dont clock on BLK and try -1 CPU -10 PCI ,-2,-20,-3-30 mine likes -2-20 or -3,-30 on high BLK 131. Also try forcing PCI ex gen 2 and see if the gen 2 codes improve things. Remember the lanes are governed by the CPU so a small boost in VTT may be necessary also. Try doing this with no CPU overclock too then you are removing more variables and RAM on XMP Rampage Tweak Mode 1.