I agree the 750a is probably a labelled third party drive. (Probably Benq, but could also be a Panasonic).
However, what really makes me go is that the 760a seems to be a ‘true’ Plextor drive. I wouldn’t have expected of Plextor to bring another ‘own’ drive. The earning margins in this market have become so small that anything small volume just is not profitabel anymore. OTOH the 716 (a, sa, al) seems to have sold in excess of 1 million pieces (cumulated serials i’ve seen). Given that Plextor is a very small player in the ODD market (and also the double price tag in comparison to the competition), that seems impressively successful (AFAIK Liteon sells more than 10 times more than that).
The website says something of an ‘evolution’, so it might be a 716a on steroids. There is mention of a new optical pickup and also ‘advanced’ inelligent tilt. So it’s definitely new hardware. Can’t wait for someone to open one of these up and have a look what chipset is beeing used.