I'm confused and also amazed to how do Sound engineering people actually re-master old music back in the 70 and re-release the high bit rate music in the form of SACD, DVD-Audio or even HDCD ?
I used to listen to old rock metal songs in cassette tape, and now in Amazon they sell the SACD version of the same title, one of the example is Pink Floyd Dark Side of the moon: http://www.amazon.com/Dark-Side-Moon-30th-Anniversary/dp/B00008CLOA/ref=sr_1_2 and this one Yngwie Malmsteen - Genesis http://www.amazon.com/Genesis-Yngwie-Malmsteen/dp/B00007AJQX/ref=sr_1_cc_1
I believe back then when I was a little boy the music was played and distributed in cassette format, and now those CD claims that sounds better than the cassette.
It's all about the entire chain. From microphone placement, recording, mixing, mastering and then your playback chain. I have heard some cassettes that sound BETTER than CD.
It used to be a dark and secretive art. No doubt there are many mastering and music restoration specialists that keep their secrets (I know I do!) but, for the most part, the entire (re)mastering process is available to known and learn.