tommyd, congratulations on your first post here at CDFreaks!
I'm sorry to hear about your trouble with burning TY CD-Rs on your PX-712.
It might not make you the tiniest bit happier to know, that I can burn Taiyo Yuden 48x CD-R media (Plextor branded) at 48x on my Plextor PX-712 with excellent quality.
But this means that there's definitely something wrong either with the media or with your PX-712. Drives use different lasers for CD and DVD so it's not uncommon for a drive to work with DVD and not with CD or vice versa.
Why don't you try some other CD-R media to find out whether the drive or the media is to blame!