Update: yup, the 7i84 was the cause. I switched the wire over to 7i77 output 01 and changed the hal line and now the drives latch on, with all the encoders working. Only X is jogging in the wrong direction.
I tried a different output on the 7i84, but no dice. There's a whole bunch of stuff on that card, anybody have any ideas on how to troubleshoot it?
I don't think I'd be able to get all the ribbon wires to the 7i77 even if I wanted to (which I don't). Should the diode next to the RJ45 socket on the 7i84 be green, or is it okay if it's orange? It's got 24V field power and has all the pins showing in hal, so what gives? I set it up to work in mode 1 for voltage output capability but that doesn't change anything. More frustratingly, it did work before (even this morning). What the heck did I do to it?