Airport Extreme - Can't Connect to Brother MFC over Ethernet

I just replaced my old reliable Linksys router with an Airport Extreme to increase coverage across our whole house. We have a multifunction Brother printer (MFC-8860DN) that is connected to the network via Ethernet. (It used to be a straight connection and now uses a Powerline to connect from the router on the second floor to the printer in the basement.) Worked fine with my Windows laptop on the old network. Worked ok from my wife's Mac on the old network -- had to manually assign the IP address each time which was a pain. At some point I think I assigned the printer to a "fixed" IP address to solve that problem.

I've now switched everyone over to the new network. On my Windows 8 laptop, I have to go in and manually assign the IP address now each time (which means going down two flights of stairs, checking the IP address, and then coming back upstairs. On my wife's MacBook Air, I can't even get it to find the printer (I go to add by IP address, it knows enough to know that I am adding a Brother MFC, but when I try to add it says the software isnt available from Software update).

All of this is a colossal pain. I like the broader coverage but it is not useful if we can't print. Any thoughts on how to solve this problem? (I tried things like Bonjour and they didn't seem to help.)

Alternatively, if I move the printer upstairs and connect to the network via USB, would that work and what might I need to do to set that up?

Finally, if the solution is abandoning the Airport Extreme then so be it.

Thanks in advance, all.