David - your last comment about "3m passive on 670s"....meaning you've had this same config and it works with a Dell, right?
This is what customer has tried:
Plugging the SFP+ cable into the X670 and the Vxrail box. No link
Plugging the SFP+ cable from one Vxrail to another Vxrail. No link
Plugging the SFP+ cable from the X670 to the Black Diamond. LINK
Plugging an Intel 10G Gbic into the X670 and another Intel 10G Gbic into the Vxrail using a multimode fiber patch cable. LINK
So I was starting to think about what Bernhard stated - trying active DAC, except there isn't any onsite right now.