Yes I do know this subject and your Plextor PX-B940SA is actually a Pioneer drive; it is the Pioneer 205 to be exact.
Read post #20 from this thread, written by cvs, one of our more knowledgeable members here: http://club.myce.com/f142/myce-presents-plextor-px-b940sa-blu-ray-writer-review-310306/
I do believe I mentioned the fact that one of the Plextor blu ray drives was a Pioneer rebadge in my first post. Nothing much wrong with that, other than much poorer firmware support from Plextor, as the Pioneer 205 is an excellent drive. But it isn't a true Plextor. They have not been made for a long time.
The newest Plextor blu ray drive is a Lite-on clone. Most of their current dvd drives are too, though I haven't tried to keep up with them all that closely. You can do a bit of reading in the forums to confirm this fact.