after reading your several format comments, tonight I compare one song 隨想曲, Paula Tsui in different format:
Regular CD 1993
20-Bit sonic solution system 1997
HQCD 2011
AMCD 2011,
SACD 2013
Regular CD, the output is medium, bass is solid, clarity is sufficient, dynamic is clear, vocal is sweet, overall warm feeling (my DENON AMP decoded playback by PCM AL-24bit)
20-Bit:, the output level is low, bass is weak, clarity not enough, no good feeling at all (my DENON AMP decoded playback by PCM AL-24bit)
AMCD: the output is loud, bass is strong, but the vocal is dull not sweet, overall flat and dull feeling (my DENON AMP decoded playback by PCM AL-24bit)
HQCD: the output is medium, bass is solid, clarity is sufficient, dynamic is good (my DENON AMP decoded playback by PCM AL-24bit)
SACD: the output medium, bass is solid, clarity is excellent, dynamic is clear, the vocal is sweet, (my DENON AMP decoded playback by DSD. not PCM AL-24bit)
My preferred choice is SACD, then Regular CD, HQCD, AMCD not impress at all, 20-Bit is the worse
So I know why those old used CD sometimes can resell so expensive
One gut feeling: new product may not always be better than the old product, it is just the excuse for the company to make more $$$