According to Intel, the ixgbe driver is designed to work with Intel® 82598, 82599, and X540-based PCI-E family of 10 gigabit adapters/controllers under FreeBSD 7.2 or later. That driver is included in FreeNAS. If for some reason, there is an issue with that particular model, create a bug report at bugs.freenas.org and post the issue number here.