What follows is an excerpt from that interview. Please follow the link for the full conversation.
PH: Who did you find easier to voice, Superman or Clark Kent?
JD: Clark Kent because he's so clearly a mask, a facade that Superman's putting on, so I didn't have to worry about being too big. I didn't want to make him ridiculous but he clearly is put on, so you don't have to worry about the realism quite so much, whereas with Superman there were a lot of moments that were pivotal and very emotional, so it was critical to not be silly. With Clark Kent you could be silly as much as you want.
PH: One thing I found is that Superman sort of walks this fine line where he wasn't exactly extremely emotional but he also wasn't monotone. I noticed at the end though where Superman was fighting Solaris it was one of the few times you really see Superman get angry. That must have been a really exciting scene for you.
JD: It was, it was fun. Andrea [Romano, voice director] is so good at pumping us up, even without seeing the animation. You can read it on the script but until you see the animation it's hard to tell how big the scene is going to be, you have to just trust her to push you, push you, push you. There's two moments when he's trying to protect Lois, with the Ultra-Sphinx and then at the end when he get so furious that Solaris killed his Sun-eater, it was fun just to blow it out, give a big growl and let him have it. So yeah there wasn't a lot of that in this film, some people were surprised there wasn't more action in this film, so those scenes in particular were a lot of fun.