This would seem to be the Holy Grail for some of us here. I have been looking for a solution for some time, without results. Here's what I have done so far:
1) I communicated with Syil America to see if they would sell me their solution separate from their CNC conversion kit. The emails from Richard were friendly, but he seemed intent on trying to sell me the complete electronic package including breakout boards, drivers, and power supply. I was only interested in the interface board that plugs in between the SX3 driver board and the front panel, but could never get a price on just that piece.
2) I also communicated with Arturo from CNC4PC.com. He has a solution for the regular X3, but has not yet created one for the SuperX3. I emailed him some schematics that user OldRaven from this board had traced out, and he seemed to think that would help him figure it out. He was also going to communicate with Seig to see if they could provide him with the necessary info. I have not seen any results from this so far.
3) There are several posts in the Syil support forum on this board that speak to this issue, but none with a solution. One user replaced the entire SX3 driver circuitry with another 3 phase amplifier that was externally controllable, but I didn't see any details as to manufacturer, cost, etc.
So apparently there are many of us waiting patiently for a true solution. Welcome to the club. Hopefully the extra noise on the demand side will prompt some more attention.