Barry's comment and the following discussion let me compare the "old" and the "new" CD of the M7 strictly. First I switched between simultaneous playing on my Pioneer multiplayer and my pure CD/SACD player. Result:
The sound was MUCH better with the real CD player independent of the CD version, any possible difference in sound between old release and box was clearly below difference of equipment. So that couldn't be a way.
Next I converted the Scherzo to Apple Lossless and put both versions to my iPod with AKG headphones. Strangely, the conversion led to files with 10% difference in size (on high level, of course). Audible result: Couldn't really hear a difference, but one could imagine the new version a bit brighter.
Finally I converted the scherzo of both versions to WAV and compared the beginning in a wave editor. And there a difference could be seen: They have increased the level in the new version! There are also slight differences in the wave forms, but this is like "find the 10 errors in the picture".
I am not an expert in this field, but I would say: it is not a remastering, but only a wave editing/emphasizing/equilibration. This might lead to a different impression when listening to it. No guarantee, that this analysis is the full truth, but it explains Barry's impression that the sound is more even (most MP3 software has a function to equilibrate levels for a selection of tracks, so maybe they put anything on the same level beforehand).
By the way, the M6, M1 and M7 (in that order) were the first CD's of these works I ever listened to. So I have some affinity to this series. And I like the M8.
Best regards
Michael