TMC429 VS SpeedyStepper

Ok this makes a lot more sense. Does the TMC429look like it will work for you? You have 4 connections to the driver chip to the motor. 2 connections from the driver to the Arduino, the Arduino just needs the connection from the marlin microcontroller. So the wiring should be 4 data on the Arduino, 2 going the TMC, then 6-8 to motors.

Library: https://github.com/Stan-Reifel/SpeedyStepper https://github.com/Stan-Reifel/FlexyStepper

I have not created schematics yet, I simply followed the specs of each boards and connected them and programmed. I will create schematics soon and share. For stepper control and connections, I used SpeedyStepper library examples here: https://github.com/Stan-Reifel/SpeedyStepper/tree/master/examples

You don't necessarily need a single shield to control them all is recommend using small, individual driver boards all mounted on breadboards honing up directly to your Arduino. Fundamentally, most stepper drivers use a 'step' and 'direction' pin, do every time you pulse the 'step' pin the driver turns the motor one position, and if the direction is high or low changes the direction the motor turns. Is suggest using a library like https://github.com/Stan-Reifel/SpeedyStepper it's very popular, way to use and there are lots of good examples. Start with getting one motor controlled how you like, then look at their examples for using multiple motors and build it up. For motor drives, you have two fundamental options: Breakout board style: https://www.pololu.com/category/120/stepper-motor-drivers these are the type that mount in most 3d printers, and are fairly compact l, but need some wiring work done to be correct. The other type is a fully enclosed type: https://www.amazon.com/Digital-Microstep-Stepper-Controller-2-phase/dp/B07YWZRXGR these are controlled in the same way but can draw much larger currents and are probably easier to wire and set up. United space is critical for you I'd recommend these. Both types are controlled with the same step direction method. I hope this helps, let me know if you have any questions