If you cut the line, I think you'd have to cut the emperor speaking over vader... it works without hims saying "Darth Vader" actually I just added it last minute becuase I thought it really pushed it and gave it an edge... without the line "How can that Be" it woudln't make sense for Palpatine to interrupt...
"He could destroy us."
"He's just a boy. Obi-Wan Can no longer help him."
"He is strong with the force."
You coudln't have him interrupt... that would be the only other thing...