I would either use a DB9 (RS485) USB to Serial Converter (if you're willing to spend a lot of time on it), a USB to RS232 Serial cable and A RS232C to 8 Pin Mini-DIN connector to make it easier on the software. I've found that when I do RS232, the software will crash on more modern computers running the software in compatibility mode, so take your pick. Good luck!
-Wyatt