What would you guy's recommend for encoders?

Depends on the electrical requirements of the enable on the AMC drive. I did not read over the doc.
How were you planning on enabling the drives and estop circuit?
I assume the enable relay called out being NC makes the drive power on only when the relay is energized and opens the inhibit line on the drive. Meaning if mesa is powered off, the normal state would be a NC on the relay which would inhibit the drive output.

Another option would be a relay on the DC Power line. You could switch it with the dedicated enable from the 7i77.

OT-CNC wrote:
Another option would be a relay on the DC Power line. You could switch it with the dedicated enable from the 7i77.

I would advise to never cut the DC power line to the drives with motors connected, that will most probably kill the drives if they are enabled.
You can switch the AC power line at will, or wire a relay to the "machine power" pin in linuxcnc and wire the drive enable relay to the "machine is enabled" pin. That is how it should be done.

Thanks tommy for the correction. On one of my machines I kill the AC to the drives via a contactor.
Worth mentioning also is to use flyback diodes if using larger mechanical relays / contactors or get relays with built in "safety circuit" that already includes a diode to prevent high voltage spike on the control circuit from damaging the opto outputs on the mesa card..