I talked to PNC at the beginning of the month and was told Samsung Pay will definitely be available sometime in December. Like you I tried to register my card and got as far as the User Agreement before it failed. Just pure speculation on my part but I wonder if the debit/credit card outage PNC...
It is an ambiguous performance and security update. 662MB in size and can be only downloaded via WiFi. If you Google search KB426709 (S6) or KB426710 (S6 Edge) it will give you more info on the ATT website.