The difference between this demo and the earlier video from Denmark is really remarkable, even if you disregard the lousy sound quality on the video. Just listen to the guitar sounds, the trumpet, the brass sections etc. When the danish guy is playing, it sounds very synthetic in my ears, far from the "live" sounds you hear on the MP3 demo.

So, my question is: Can we expect this sound quality when playing "live" using the arranger functions, or is this demo made using the sequencer with a lot of optimizing and tweaking of each sound afterwards?

If the MP3 demo really shows the quality we can expect when playing live, then I have this advice to Korg: Get a demo guy with show qualities similar to the guys from Yamaha (for instance Michael Voncken or Bert Smorenburg). Then make some high quality videos with him showing the features and sound quality of the board, and publish them on the net. The marketing value would probably be enormous.