Nice of you to keep us updated, many don't take the time, I consider this rude.
I believe you are referring to your stand alone DVD players getting hot, i think Rolling 56 thinks it's your Pc's DVD players, if I'm not mistaken you only have the Plextor px 716A, please clarify.
I'm not convinced both your DVD players are at fault, one possibly, but two seems unlikely. Seems like a media problem in my opinion. Not being familiar with Buffy The Vampire Slayer, are these 4 episodes on an original?. If so, do you still have the original?
To troubleshoot, if you have the original, and it doesn't freeze on either of your DVD players, then it's your backup copy that's the problem. Although perhaps time consuming, one more way to test is to put your backup into someone else's DVD player.