Hi all!
first of all... thanks to Howard and Khalid for their precious and helpful work!
I have recently upgraded my Onstep gear with new Fysetc S6 v 2.0 and TMC2130 SPI with success thanks Khalid instructions on wiki page.
I use Onstep since 2015 (arduino mega version with TMC2100) on my Eq6 with sanyodenki steppers and belt transmission...this is my pictures taken with it. https://www.astrobin.com/users/CarCarlo/
This is an old post but i want to share my experience in putting the board in DFU Mode and uploading firmware using Linux.
I figured out that if i connect GPS nema Module to SoftSerial2 (RX2/TX2) on Fysetc S6 i can put the board in DFU mode without disconnect power on GPS module.
The  2.0 version of the mainboard does not have boot0 push button and instead of this FysetC has changed it with a 3 pin. This helped me to put a on/off switch outside the box for simplicity.
 
I hope that this can help...

CS
Carlo