"... but not on a gigabyte switch. "
I have mine on a Gateway Gigabyte switch, and it works fine (but at 10 base T speeds, of course). Is it possible your switch does not support the transfer of AppleTalk [over EtherNet] packets? Some wireless switches from PC-centric companies do not support AppleTalk packets.
The logic board swap is pretty simple, except the clearance to the worksurface is tight, so do not try to slide in the board with the printer sitting on the floor. Get it up on a table where you can see it, and consider tilting it or lifting it up on blocks while you insert the new board.