In my opinion, the blu ray release contains the best audio so far.

The original 60s cartoon 5.1 basically puts the music and sound effects synced mostly between the front and rear speakers. However you do not hear any dialog/vocals on those speakers, only the center channel which attempts to isolate the dialog as best as possible.

The 1992 XMas again cartoon bonus material on the bluray is also mixed in 5.1 but the stereo FL FR channels are a stereo mix of all vocal/music/effects while the center tries to isolates Vocals (though not as good as the 60s classic attempt)

However the rear speakers in “Xmas again” is just the music with no sound effects or dialog which is a minor step above from the classic if they didn’t add a silly reverb effect to the back which is mostly noticeable if you just want to isolate those tracks to try to listen to the score only.

Now the DVD the bluray package comes with is no different than any previous DVD attempt. Both cartoons on the DVD are 100% mono 1 channel.

In short:
Bluray = Fake 5.1 but centered dialog / Stereo
DVD = mono

In addition, both cartoons are 4:3 on the bluray but still in great quality.

Edit: A personal Charlie Brown / Audio goal is to get a copy of “Bon Voyage Charlie Brown” in some form of stereo or 5.1 attempt. There are a couple of soundtrack pieces (some james bond sounding but also the snoopy bar scenes) that I would love to hear just the music to. To my knowledge all VHS/DVD releases have been in Mono.