The new stuff is also from the movie. The way it seems is that they put all the best stuff on the main soundtrack and left the second disc for the extra stuff that didn't fit, basically for those who are die hard and want to hear it all.

One of the extras that's on the new one is the credits music which you can already listen to if you watch the movie. The rest is recognizeable from various parts of the movie but from what I've heard so far (I haven't listened to the whole thing just yet as I bought a few other soundtracks recently also) the other tracks are similar to what's already on the main disc.

As for the remixes, they actually aren't bad at all. I kind of bought the second disc thinking "Oh well, I'll just uncheck the remixes so I don't hear them when I listen to this" but curiosity got the best of me and they are actually pretty cool. I was a little concerned about the techno/orchestra mixing together as well and thought the style just wouldn't work well but these actually turned out quite well. I'm somewhat of a techno fan in general though. If you absolutely can't stand techno then you might not like them as much or at all.