Use an Arduino Mega(or clone) and a RAMPS board to take the input from Marlin's Extruder selection(1 to 3 bits) plus Enable, Step and Direction and feed it to the on-board RAMPS stepper drivers. Also for more, output additional Enable, Step and Direction on the expansion header to use off-board stepper boards. And as an extended goal, be able to do initial setup using SPI for the TMC2130(and provide CS Pins)