PX-750a can't quality scan?

Nero Start button grayed out and I can’t create a test disc, nor do a quality scan. Does this drive not support scanning, like other 7 series Plextors?

No it cannot.

The 750 is not a drive developed by Plextor and as such not part of their “Premium” drive line. AFAIK the 750 was developed by Teac (model 516E, i think) and produced by Benq, who also sold this drive as their 1670 model. It uses Panasonic electronics which doesn’t allow for quality scanning.