I have no 5.1 system, so I limit my observations solely to the remastered stereo version on this boxed set.
I write having again listened to a side by side comparison of my copy of the 1973 orginal against the remastered 2009 and I do not feel I will bother listening to the 2009 version ever again. For me the sound is simply so "tidied up" that it sounds dull - I mean the frequency extremes just don't seem to be there, nor do the more dynamic sections get at all dynamic.
The remastering also has changed the emphasis on the instruments, with the bass far more prominent in many places and, at times, an apparent attempt to simply the sound has meant some instruments disappearing. Since I love the orginal, I admit that it is difficult for me to accept these revisions as in any way an improvement.