I have several of those "remastered" RCA Living Stereo multi-channel SACDs, I might be wrong here but I don't believe they are exactly remastered per se, but instead they used the original three channel masters that were done when they were originally recorded. RCA was forward thinking back then. A lot of these were recorded even before stereo records hit the market in '57. When stereo hit, they were down mixed into two channels because, at the time, that's all the current consumer playback technology had.
They still sound pretty durn nice though, particularly when you consider many were recorded over 60 years ago.
