edit: guess I missed a few posts before posting.. but yeah, you don't 100% HAVE to use their adapter, but you'd have to convert from TTL to serial then serial to USB on your own if you don't use theirs. Way easier to just use their adapter.
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I have one of the cables already..
PLX sells a cable that converts their output (whatever it is) to a USB plug. It basically converts TTL to serial then has a built in serial to USB adapter.
It shows up as a COM/serial port when connected to a computer, which is exactly what you need
http://www.amazon.com/PLX-Devices-iM.../dp/B00JF73VUU