ok, i think i worked this one out too. the z connects to a pin directly with a pull up resistor (dont know how i managed to miss that before) and the X and Y ports connect to the same pins as their respective stepper drivers stall detection pins. these are switched with a BL1551B electronic switch (kind of works like a relay but i have no idea how since its not magnet based). these switches are controlled by both the dip switch on the board and a digital pin on the STM. that means that in theory you could use them as digital pins for input then switch them over while homing although i dont think this is a good idea.
i will do a full write up on this at some point but i have also emailed sovol to ask for the schematics or a true pinout diagram (not sure why i didnt do that earlier) so if they come back and send me anything useful ill use that instead (and post it somewhere)