After assembling the PCIe card I was luckily surprised that my kernel brought up the NIC without any difficultys, so I plugged my SFP+ modules into the server, only to be greeted with:
ixgbe 0000:24:00.1: failed to load because an unsupported SFP+ module type was detected. ixgbe 0000:24:00.1: Reload the driver after installing a supported module.
Yay. After 2 hours of useless googleing I asked a friend who happens to be a linux kernel maintainer, and luckily he knew just the fix therefore:
All you need to do is add a file to
options ixgbe allow_unsupported_sfp=1
And reload the ixgbe module:
modprobe -vr ixgbe modprobe ixgbe
Easy as pie, at least if you know how.