Seems like a mirror of the Plex 708A firmware. [the install app even has the plextor “P” logo in the upper left corner.]
Available here: ftp://www.tdk.com/software/DVDRW840G_103.exe
IndiDVD 1.03 Firmware Upgrade - Click to Download
Provides greater compatibilty with various DVD Media
Download Firmware 1.03 to Desktop
Doulbe click on DVDRW840G_103.exe
Cick on OK. and choose the TDK DVDRW840G drive.
Click Update to start the flashing process.
If asked, let the computer reboot or left click Exit on the flasher program when the flasher program is completed.