I have a 716sa and lost my Plextools disc, the plextools website only offers XL which is not free and the Pro upgrade, where can I just download the regular pro?
You can't download it legally for free, since Plextools Professional (non-XL) is also commercial software... you need to buy it again at PlexTools website.
Is there a non-professional?
No. Previous versions of the software do exist, but they are no longer mantained and do not support current drives, so they are useless.
As an alternative maybe askin plextor, perhaps they're so kind to send you a new disc of course for free, saying you've lost your disc etc...
In Europe they might indeed to that