Adywan, I ask you to reconsider using GM's idea. I bet the difference in delivery for "How is that possible" can be fixed, after seeing the improvements in Vader's voice in SW-R.
I really like GM's proposed dialog. The interruption is great, as well as the use of Palpatine's "Lord Vader" in an almost condescending manner. The original dialog was great at the time, but I think it needs to be updated to match what we now know of Palpatine's scheming personality. A shot of Palpatine sitting in his office afterwards grinning to himself would be the icing on the cake!
As far as the rule of two, let's look at what's in the movies (forget the novelizations and all the other EU crap). The only people that we see who are aware of the rule are Yoda and Mace. From that scene in TPM (I'm going from memory here), it's not even clear if Mace was aware before Yoda said anything. My point is, it may not be common knowledge for the Jedi, and Anakin may not even be aware of it. So Vader's desire to make his son an "ally" - as far as he knows - may not be an outright declaration of war on Palpatine. Regardless of whether Palpatine knows of the rule (he probably does), he's now just had a revelation that Luke could be a good replacement for Vader. If you think about it, why would Vader hand over his son to the Emperor in ROTJ if he KNOWS of the rule of two? Why would he willingly send his replacement to the Emperor?