After playing a few hours of these songs, I can say what Astat has said will make me believe that Harmonix change a bit of these songs to throw away the audio fans from taking the multi-tracks.
Each song sounds a bit difference from the original. Mostly due to the fact of adding the keyboard peripheral.
Certain sounds of the song get amped up to make the keys sound like a huge part of the song.
Now I have played each instrument in the game to hear the difference in the sounds for each and after playing as a Band. The little tweaks are still present.
Thers is nothing in here that ruins the songs but some might find it a bit odd.
For example SIB has the keys in the game sound a bit weird? Can describe it but once you play it or hear it you'll notice.
For ITE there is static around Mike verses to give a bit more sound effects for the visuals when playing the game.
In Numb chesters vocals get a little bit more reperated to where you can notice each layer of his parts, which is a plus when playing in Harmonies.
And for WID Mikes na-na-na's at the end are amped up a bit more to help with the Harmonies which is a plus for me.
All in all the songs work great in RB3.
Keyboards are amped a bit to make the player feel a bit more important. Lol
the guitar, bass are bit stale to play (but we all knew this) when coming into playing for RockBand3
Drums are what I enjoy, so they are great.
Voice is what I have been waiting for and these songs helps me with LP fix for RB.
That is all for now. Lol