I was having some trouble with my PX-716 after upgrading from FW 1.02 to 1.03. High quality media (such as MCC004) that had worked before, now had very strange burns. Previously, I always did a TE/FE of every media I tested before burning, but never really thought much about it. It wasn't until I noticed some comments in the latest beta firmware thread that I realized what was going on: the PX-716 requires a TE/FE scan of ALL media--even known types--to recalibrate PowerRec after every firmware upgrade.
Below are a few before and after samples of MCC004 burned at 16X. Please note that the TE/FE test indicated that the media should not be burned at the highest speed.
At any rate, the moral of the story for the PX-716 is, TE/FE each of your disc brands before you burn them after an upgrade. This appears to be true for the beta firmware as well.