Board Selection For Closed Loop Scale Feedback?

Hello,

I have been looking to build a CNC machine for some time now. I began collecting parts before realizing there would be difficulty collecting certain parts.

The primary oddity of my design is that it is designed to use 1um magnetic scales for closed loop positioning feedback. My understanding is only LinuxCNC can handle this. Thus I am looking at LinuxCNC boards.

4x Stepper motors (Nema 23)
4x Digital controllers (DM556T)
3x 1um magnetic scales (Ditron heads TTL/RS422 output)

It seems that the 7I95T would be ideal but is out of stock.
I did not purchase a 7I97 I could have as it appears it would not be able to send the digital signal my stepper controller expects.

Am I essentially in a waiting game, spending many times the money, a HW redesign, or a roll-my-own electronic HW interface?

Another option is the Pico Systems Universal Stepper Controller, which is in stock. It can accept encoder inputs (or run open-loop) and uses the parallel port to communicate with the computer. (Full disclosure, I make these.)
Jon

Thank you both for the options and quick response. I'll look over them.