ON THIS PAGE is where you can request a SDK from Plextor, but I suspect that again, it is the Linux SDK that they are talking about (the Windows version seems to be an internal SDK for partners only, unlike Linux GPL). I Quote:
"Article ID. M402U0027
How can software developers get the SDK for the PX-M402U?
Please send a request to info@plextor.com requesting the SDK. You will need to sign a software license agreement and then the SDK will be distributed to you. Alternatively, you can request the SDK directly from WIS Technologies, the developer of the encoder chip used in the PX-M402U product. (http://www.wischip.com/prod.html)"