It is seen by Intel82566MM.kext, but doesn't show up, doesn't work.

I'm assuming because its a full featured NIC with every option under the sun, TCP offload, iSCSI boot, SR-IOV(hardware virtualization support so every VM can use the NIC without extra overhead/IO losses) etc....

Intels page for 82576:
http://www.intel.com/products/ethernet/res...76EB&s3=all

Intel also has FreeBSD driver with source.
http://downloadcenter.intel.com/Detail_Des...D*&lang=eng