In case anyone needs this as well, sharing a guide how to replace stock drivers with TMC2208.
I haven’t tested them long enough, but they are absolutely quiet, which is cool and that makes a lot of difference 
So some good resources to go to:
- video how to replace old drivers with TMC2208, most important takeaway - pay attention to their orientation - i.e. make sure DIR and GND pins get to same pins as with previous drivers. Replace when farmbot is powered off.
this table shows jumper configuration for various microstepping setups for both old and new drivers - I went for 2 microsteps per step
my settings before:
my settings now: (you need to set microstepping properly and invert motors)
so far so good, although I have some things to test & followup:
Torque (vs microstepping)
- I suspect the new drivers might have a bit less torque. I have more issues to dig into soil with weeder tool - but - other factors might be influencing this - (soil was more wet and I have changed the tool to bear only the largest blades so it takes more power to put it into soil) Does anyone know (is there a tradeoff between torque and microstepping?)
Thermal management
- TMC2208 have bigger heatsinks and get more hot than the old drivers. Many sources on the net suggest usage of fans. No issues so far, but not enough testing either - and hot season is still about to come. For the time being I kept minimum microstepping (not sure if more microsteps lead to more heat though). Also the voltage is not higher than 1.1 V - not sure if I can set it all the way up to 1.9 V as with the old driver (and if that would create better torque)
if someone knows answers to the above questions - it would be lovely to hear your suggestions