Barry,

I am one of the few people that implemented encoders on my mounts.  I have a couple of Losmandy mounts with Astro Devices 311,296 step encoders.

I am driving them through a Teensy 4.0 that is also my wired Ethernet connection.  I originally was using a Teensy 3.2 for that internet and encoder interface, but had to make the 4.0 work because the 3.2 could not keep up with the pulses during a slew. I have some serious doubts if any of these processors will track properly with a 10 million tick encoder (about 30x as many pulses as I see) while also running either Wifi or Ethernet links.  Should not be an issue at tracking rates, but if you connect these be certain to test how your slews work carefully.  When I was using the Teensy 3.2 the OnStep would think it has moved about 1/2 as far as it actually moved.

John