Well, I screwed up, thought I found the perfect motherboard, didn't look closely enough at who made the Lan chip.
Apparently Asus are supplying their -MX boards with the Attansic Lan controller. Linux users have discovered this too and there is a driver for it.
I know nothing about Linux but was wondering if it was possible just copy the driver onto the UnRaid USB drive and all would work, or is there more to it?
http://www.linux-tested.com/results/asus_p5ld2_mx.html
"The On-Board Attansic L1 Gigabit Lan chip was not detected by normal install. Download the driver file atl1-x-x-x.tar.gz then install it."