So two years have gone by and I have not done a damn thing with this, just sitting in my living room collecting dust. Now that I am gainfully unemployed again I have some time to mess around with it.
So, where did I leave off.. Oh yeah, filtering the PWM. Well, that was a mess. I couldn't get a stable drive signal out and the controller started acting up, it was replaced and I never touched it.
I decided a few weeks ago to mess with it some more, I went with plan B this time, directly coupling an encoder to a small Escap motor to a CUI 2500 line shaft encoder act as a kind of integrator. I then tapped into the single ended encoder signals back to the controller with a 26LS31 line driver. This sends a differential signal to the mitsubishi servo drives which are set up for encoder follow mode.
It works! Now I need to finalize the encoder tap and mount everything down as well as program in all the parameters specific to the mount.
In the image below you can see the motor-encoders on the left, the mess of wires on the breadboard is the encoder tap and the black box below that is the SiTech telescope controller.