5x10 servo router rebuild - analog of step/dir with mesa card?

I've got a 5' x 10' CNC router with a failed Mach 3 control. It has Yaskawa Servos (SGMGH-09ACA61) and was set up for step/dir with an ethernet smooth stepper. It was "open loop" with that control. It has four motors for the 3 main axis and a 5th motor for a rotary axis. I might not use the 5th axis but I do have a crazy idea for an automated dust collection "axis" that would probably use stepper motors. 

I have a Mesa 7I76e that I bought several years ago for another machine that has yet to be completed and I think this would be my fastest/easiest control to drop in but would still leave me open loop to the control. Instead I've been thinking of running with analog servo signals and the encoder feedback into LinuxCNC using a 7I92TF with a 7I77 or a single 7I97T. It seems the 7I97T might be a bit light on general I/O since the machine has an ATC spindle and several other pneumatics that need to be controlled and sensed so I'm leaning towards the former combo. 

Any suggestions wrt to Mesa card availability and the advantage of using analog vs step/dir in this application? 

 

I would think that leaving it step/dir would be the easiest path
and would require few wiring changes. It also would not require
changing the drive setup, tuning the drives or tuning LinuxCNC's
feedback loop.

The only real advantage to an analog setup is that you can disable
the drives without losing position.

Do the servo drives have encoder outputs? Al Yaskawa i have worked with do have them, so since you have 7i76E just add a 7i85 or 7i85S for encoder feedback and you get the best of both worlds, easy tuning and position control even when drives are disabled.

Pardon my ignorance... Based on your comment I presume that the servo tuning is stored in the servo drives?

I have had the understanding that I DO want the LinuxCNC feedback loop in order to make a [more] closed loop system which is more better than having the control completely blind to the position (or loss of position) of the motors.

Yes, the servos have relative encoders. The previous owner of this unit had always planned to upgrade the control so that the encoders would be useful. It makes sense to me as well.

Since the 7I76e variants are not in stock right now, and my other machine that I will eventually build is a stepper motor machine, would it make more sense for me to buy one of the analog boards that are in stock right now? I suspect that some more snooping around the Mesa store might be in order...

7i96S + 7i85 or 7i85S and add a 7i84 if you need more IO.
Later, when you do feel confident to dip your toes in analog territory you only need to get a 7i83.