The meters are updated once for each buffer. So that’s why they are slow to update with large buffer sizes.
What screencast program are you using?
I have been checking out various screencast recorders these last few days, and I found that BBFlashback Express (freeware) has an option to record the soundcard output, although that didn’t work for me.
With my RME soundcard, I’ve physically cabled the audio output back into a stereo input. With the RME mixer software I can route the mic directly to the output, so I’m able to record both the mic narration and playback in Podium (with ASIO).