Found this supermicro which would be a DREAM to run as the backbone router/firewall. Add in something for coax, fiber, or adsl and you got a perfect modem/router/firewall.
It is the mbd-a1sri-2758f-o, 8-core avaton, up to 64gb ecc, four gigabit off the c2000 avaton chipset, supermicro ipmi, runs ~$300-340 usd. Saw one used on amazon for $220
*Nerdporn nosebleed* This thing would FLY as a backbone router.
And if you look closely - usb3 internally on the board. Pfsense on a usb stick, then you can write off the logs to the nas. (That's what I would do anyway, maybe throw in a tiny 2.5" hard drive or ssd for caching)
A less expensive alternative.
Jetway nf9hql-525, $150-200
What's awesome about this one is it has a cf card slot on board. Perfect for a tiny installation of pfsense or clearos. It's not an avaton, but a dual-core atom, so no ecc. Usually don't need much more for a SOHO environment, and it will still run circles around most pre-built solutions from the likes of cisco, tp-link, etc.
The quad-core avaton board from asrock would work fantastically, too, but if you have more than 1 network you're trying to route internally you'll need another gbe controller card.
It'd be nice to see more competition in this market. :/
Maybe someone can release an itx board based on arm with tons of ethernet ports.