As a final update, the N810 has connected (I'm not going to bother trying with the 770 'cause... well... the N810 connected).

I disabled DHCP and entered a manual IP. Very odd that the only two devices that couldn't connect were the NiTs that've been sitting unmodified in a drawer for months. (My router setup hasn't changed in about a year and a half). Maybe it's starting to go.

Anyway. There's my solution. Seeya again in a few months guys.